Effect of Time of Year on Average Daily Gain of Feedlot Finished Bison (Bison bison)

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Bruce D. Rutley and John S. Church

Abstract

Seasonal effects on the average daily gain of 275 grain finished bison bulls that entered the Bison Evaluation Unit (REV) at various dates between the fall of 1992 and the spring of 1995 were assessed. Average daily gain was higher in the spring (1.1 ± 0.04 kgd^-1) than in the fall (0.706 ± 0.05 kgd^-1). In addition, the average daily feed consumption per animal was greater in the spring (14.30 ± 1.15 kgd^-1) than in the fall (10.64 ± 1.15 kgd^-1). A warm-up period was demonstrated to be beneficial to average daily gain. Bulls that were not warmed up had an average daily gain of 0.86 ± 0.02 kgd^-1. Bulls that were warmed up for a few days (<50) gained 1.1 ± 0.10 kgd^-1, and bulls that were warmed up for more than 50 days had the highest average daily gain (1.5 ± 0.07 kgd^-1). Mixing small groups of bulls from different herds for the purpose of filling the pen was shown to be detrimental to average daily gain. Groups of four or more gained significantly more (p<0.05) than groups of three or less, when mixed in the same pen (0.68 ± 0.03 kgd^-1 vs 0.36 ± 0.4 kgd^-1). Feed conversions ranged from 9.9 to 16.6, but there was no statistically significant difference in total feed conversion between the spring and fall seasons. These results suggest that there is a slight advantage in grain finishing bison in feedlot in the spring rather than the fall season.

Background

The plains bison has been farmed or ranched since before the turn of the century when the species was rescued from extinction (Roe 1970; Dary 1974). At one time, considerable interest was shown in the bison as a species to hybridize with cattle and Agriculture Canada conducted research from 1917 until abandoned in 1965 (Peters 1958, 1984).

A resurgence in interest to farm bison occurred coincidentally with: 1) bioenergetics, metabolism and digestion studies (Richmond et al 1977; Christopherson et al 1977 & 1978; Schaefer et al 1978; Christopheron et al 1979a & b); 2) demand for lean red meat; and 3) a search for more suitable forms of northern agriculture. This renewed interest resulted in considerable growth within the Canadian bison industry -especially in the Peace Country. In 1985, three Peace River region commercial herds farmed less than 150 head compared to 54 producers ranching 8820 head (prior to calving) in 1992, while the Canadian bison herd increased to 18,400 by October 1992 (Rutley 1992c). It has been estimated (Hussey 1991) that if nothing limits industry expansion that the national herd will be 120,161 by the year 2000.

Industry development has occurred in absence of applied scientific research. Bison research within the park herds has been ecological and zoological in scope (McHugh 1958; Roe 1970; Meagher 1978; Telfer and Carins 1979; Reynolds et al 1982; Hawley 1987; Reynolds and Hawley 1987; Hawley 1989; Meagher 1989) and provides little suitable data for current specific industry development questions related to finishing market bulls. The techniques that have enabled the bison industry's expansion were developed on an individual, ad hoc basis and are described in publications of the American Bison Association (1993) and the National Buffalo Association ( Dowling 1990).

Limited empirical data is available for the commercial bison producer finishing bison for slaughter, however the commercial bison industry has been routinely finishing bison for regional, national and international markets. Gain of feedlot finished bison bulls in the scientific literature is limited to: 1.4 lbs. and 1.l lbs. per day for males and females, respectively (Peters 1958) and 0.76 kgd^-1 (Koch et al. 1988). Hawley (1986) reported slaughter characteristics for 6- 2.5-year-old bison steers, but not ADG during the 78-day finishing period. Expected gain and finishing rations have also been published in the bison industry publications (Dowling 1990, American Bison Association 1993) and by Rutley (1992a). Reports from scientific studies of grain finishing of bison bulls as practiced by the members of the Peace Country Bison Association (PCBA) do not appear in the literature.

Recent developments in the marketing of bison meat has resulted in demand exceeding supply. These market developments have occurred coincidentally with forwarding young bulls to the prime meat market, grain finishing and utilization of the newly developed Canadian Bison Grading System (Rutley 1992b). Therefore, the need for research into finishing of bison bulls was identified as a priority of the PCBA.

Observations made by PCBA members and preliminary research conducted at the Centre for Agricultural Diversification indicated that bison bulls were gaining at different rates depending on time of year started on grain finishing (Rutley, unpublished data).

Bulls started on grain finishing between mid February and mid October gained at a faster rate and the cost of production was half that of bulls started on grain finishing between mid October and mid February. This data was collected from bulls that were not part of a formal controlled study. However, a reduction in metabolic rate in bison under cold temperatures as described by Christopherson et at (1978, 1979b) may provide one possible explanation for a potential seasonal effect on average daily gain.

Implications on industry development were considered sufficient to warrant a study on the effect of time of year on average daily gain of feedlot finished bison. Quantifying any differences will enable producers to plan management programs economically.

Introduction

Grain finishing of bison in the Peace Country involves placing groups of young bulls (18 to 30 months of age) into a restricted area (feedlot or fieldlot) where they have access to grain and dried forage free choice. Grain fed consists (primarily) of whole oats, whole oats and barley in combination at 75%-25% or 50%-50%. Dried forage consists of fescue, barley or wheat straw and occasionally good quality grass hay.

Prior to 1992, very few producers finishing bison bulls had or used weigh scales, therefore rate of gain in the feedlot was unquantified. Rutley (1992a) reported gain between 0.56 and 1.04 kgd^-1in four groups of bulls. Individual average daily gain ranged between 0.45 and 1.09 kgd^-1 over a 180-day feeding period with interval gains ranging from 0.15 to 2.38 kgd^-1. ADG of bulls based on month of entry were: 0.68 kgd^-1 (January); 0.59 kgd^-1 (February) and 1.02 kgd^-1 (March).

Development of a steady meat supply to fill the increased demand for bison meat is required. Having identified differences in rate and cost of gain by season, there was a subsequent need to quantify those differences to determine if any modification to the present system of placing bulls on feed as they reach a given age/weight is required. Therefore, the goals of this research were to:

determine the effect of time of year on average daily gain of feedlot finished bison;
determine if the effect is repeatable (i.e. repeat study a second year);
calculate the differences in cost of production associated with season; and
if differences are substantial, calculate the cost to the industry and recommend changes

Methods

In cooperation with PCBA members, bison bulls between 18 and 30 months of age and over 350 kg entered the Bison Evaluation Unit (BEU) at the Center for Agricultural Diversification. Two hundred and seventy-five bulls from approximately twenty separate herds entered the BEU between the fall of 1992 and the spring of 1995 so that average daily gain during grain finishing could be evaluated. The bulls were weighed at entry, and if necessary, they were retagged, dehorned with a veterinary dehorning saw and given an injection of ivermectin at cattle dosage rate and placed into one of two groups of approximately 20 bulls.

Bison would have free choice access to a standard ration of rolled and blended oats and barley (50:50 or 75:25), good quality fescue or barley straw, cattle mineral and water. The composition of both the 50:50 and the 75:25 ration are outlined in table 1.

Grain was fed in a portable bison grain self feeder, hay available from a tombstone style round bale feeder, mineral available in tubs mounted on the end of the grain feeder and city water available from waterers (hog style).

Table 1: Composition of 50:50 and 75:25 ration as feed

	50:50 ration	75.25 ration
Moisture %	12.6	16.3
Crude Protein %	10.1	9.3
Calcium %	0.10	0.08
Phosphorus %	0.31	0.28
Potassium %	0.38	0.38
Magnesium %	0.10	0.10
Sodium %	0.03	0.01
Salt %	0.07	0.03

Bulls were housed in four large pens with packed sandstone shale for footing.

Dividers between the pens were either planks or wire fence with plywood hung as a visual barrier. No additional shelter was provided. The pens are located adjacent to the Canadian National spur line into Dawson Creek.

Bulls were placed on a formal 90-day feeding period that would commence in November 1992, June 1993, November 1993 and June 1994. Bulls were supplied by members of the PCBA who retained ownership of the animals throughout the trial. At the end of the 90 day feeding period, the owners were free to market their bulls as their markets demanded. Bulls were placed into pens which served as replicates. Essentially, two experiments were conducted in total, in successive years (table 2 and table 3). Two different rations were used between years. Furthermore, the average daily gain in four additional pens that were observed for a longer duration was also compared (table 4).

Table 2: Experiment 1 (Fall 1992 – Spring 1993)

Season	Trial Start Date	Pen (Replicate)	n	Ration	Forage
Fall 1992	12/9/92	1	28	75:25	Fescue Straw
	12/3/92	2	15	75:25	Fescue Straw
Spring 1993	6/29/93	1	24	75:25	Fescue Straw
	6/7/93	2	15	75:25	Fescue Straw

Table 3: Experiment 2 (Fall 1993 – Spring 1994)

Season	Trial Start Date	Pen (Replicate)	n	Ration	Forage
Fall 1993	12/22/93	1	11	50:50	Barley Straw
	12/22/93	2	23	50:50	Barley Straw
Spring 1994	6/6/94	1	19	50:50	Barley Straw
	6/6/94	2	21	50:50	Barley Straw

Table 4: Additional groups observed

Season	Trial Start Date	Group	Pen	Ration	Forage
Fall 1994	11/24/94	P1	Field	Oats	Grass hay
	11/24/94	P2	Field	Oats	Grass hay
	8/21/94	NT	1	Start on Oats, then 75:25, then 50:50	Grass hay
Winter 1995	2/1/95	M	2	Start on Oats, then 75:25, then 50:50	Grass hay

Handling facilities consisted of a half-circle tub complete with three boxes, palpation cage and bison squeeze (Hi-Hog Farm and Ranch Equipment Ltd.). Body weight was collected from a Senstek D-2000 electronic scale placed under the first box (Year 1) or in the half circle tub (Year 2). Neither feed or water was withheld prior to weighing.

Calculations

All data and calculations for ADG, grain, forage and mineral consumed are based on the 90 day feeding period, unless otherwise stated. No attempt was made to quantify water intake.

A. Average Daily Gain: average daily gain is determined by the difference between current weight and previous weight divided by the number of days in that interval. Bulls were to be weighed on entry, at Day 0 if different than entry, at Day45 and Day 90. The results are presented as individual average daily gain from Day 0 to Day 45 (ADGSM: Average daily gain.start-middle), Day 45 to Day 90 (ADGME: Average daily gain.middle-end) and Day 0 to Day 90 (ADGSE: Average daily gain. start-end) for experiments 1 and 2. Groups described in table 4 did not have a mid period weight, therefore ADG was determined as current weight less start weight divided by the number of days in that interval.

B. Average Daily Grain Consumption: grain self feeders were routinely weighed prior to entry and on exit from feedlot pens using commercial scales available at the adjacent South Peace Seed Cleaning Plant (SPSCP). Grain consumption was determined by difference. Average daily grain consumption was determined as the total grain consumed divided by number of days between weighings. Average daily grain consumed on an individual basis was determined by dividing the average daily grain consumed (by the group) by the number of head within the group. If bulls were removed from the group between weighings, average daily grain consumed per day was calculated by using the number of "bull days". This results in an average per head consumption and assumes equal intake.

C. Average Daily Forage Consumption: since forage was available for consumption from round bale feeders and there would be no accounting of daily waste, ADFI is more adequately described as Average Daily Forage Used. Sample bales from each lot were weighed at the SPSCP commercial scale to provide an average weight. ADFI was calculated as the total kg forage fed between two given dates, divided by the number of bull days. This results in an average per head consumption assuming equal intake.

D. Average Daily Mineral Consumption: calculated as mineral consumed between two given dates divided by the number of bull days. This results in an average per head consumption and assumes equal intake.

E. Average Daily Total Combined Feed Intake: calculated as the total of average daily grain consumption and average daily forage consumption.

F. Feed Conversion: total grain feed conversion was calculated as total average daily grain divided by total average daily gain, total forage feed conversion was calculated as total average daily forage divided by total average daily gain and total combined feed conversion was calculated as total average daily forage and total average daily grain divided by the total average daily gain.

Data was compiled and entered into a computer based record system (MSWorks), edited for completeness and verified for accuracy (MS Excel) by reconciling raw and entered data. Statistical analyses were conducted using the repeated measures analysis of variance option of Abacus Concepts, SuperANOVA (Abacus concepts, Inc., Berkely, CA, 1989). Season, Pen, and Year were entered as independent variables into the general linear model, with initial body weight entered as a covariate. In most analyses, individual animal was the experimental unit. In analyses which involved either consumption or conversion, the individual pen served as the experimental unit as grain, forage and mineral were measured on a per pen basis.

Results

Feed Intake

The total amount of grain consumed, forage consumed and mineral consumed per pen is outlined in table 5. In general, there appears to be a trend towards higher total consumption of grain in the spring than in the fall on a pen basis. Because there are different numbers of animals in the individual pens; however it is more appropriate to look at the consumption on an average per animal basis (table 6) in order to determine true differences.

The average daily grain consumption/animal, average daily forage consumption/animal, average daily mineral consumption/animal and the average daily total combined feed consumption/animal for animals on the 90-day trials is shown in table 6. Bison tended to consume more total feed in the spring than in the fall. In the spring of 1993 bison consumed 16.0- 16.4 kg of total feed per animal daily, compared to 7.2- 10.0 kg of total feed per animal daily in the fall of 1992. In 1994 bison consumed 12.4- 14.1 kg of total feed per animal daily compared to 11.5 -13.9 kg of total feed per animal daily in the fall of 1993. Bison consumed more mineral daily (0.04- 0.06 kg) in the spring than in the fall (0.02- 0.03kg).

While there is a trend towards increased grain and forage consumption in spring opposed to fall, neither average daily grain consumption/animal or the average daily forage consumption/animal was significantly different between seasons (table 7a, table 7b). However, the average daily combined feed consumption/animal (average daily grain consumption/animal + average daily forage consumption / animal) was significantly greater (p <05) in the spring than in the fall season (table 7c, figure 1).

The total grain feed conversion, total forage feed conversion and total combinedfeed conversion is shown in table 8. The total grain feed conversion per pen is similar between pens and between seasons. The total grain feed conversion per pen ranges from 7.2 to 10.8. The total forage feed conversion per pen and the total combined feed conversion per pen had a much broader range, from 2.1 to 13.6 and 9.9 to 22.5 respectively.

There were no statistically significant differences (p<0.05) in the grain feed conversion (table 9a), in the forage conversion (table 9b), or the total feed conversion (table 9c).

Average Daily Gain

The average daily gain for each group (by pen) is outlined in figure 2. In experiment 1 and 2, ADG ranged from 0.92- 1.68 kgd^-1 in the spring compared with 0.58-0.87 kgd^-1 in the fall.

Average daily gain was significantly greater (p<0.05) in the spring than in the fall during both experiment 1 (Fal11992 -Spring 1993) and experiment 2 (Fal11993 -Spring 1994) (figure 3). Average daily gain for bison in the spring was 1.13 ±0.04 kgd^-1 while in the fall the average daily gain was 0.71 ± 0.05 kgd^-1

One pen had a higher ADG than any of the other pens (1.68 kgd^-1, Spring 1993, Pen 2). This group had a longer warm-up period (117 days) compared to all other groups. Although this group also consumed more grain (11.8 kgd^-1, table 7) than all other groups, this group still had the lowest feed conversion ratio (9.9, table 6).

Table 5: Total average daily gain (kg), total weight gain (kg) and total feed consumed (kg) per pen.

Year	Season	Pen	Ra- tion	Days	# of Bulls	Total ADG	Weight Gain/ pen	Grain Con- sumed	Forage Con- sumed	Mineral Con- sumed
1992	Fall	1	A	90	28	0.87	2154.5	18673.2	6414.8	59.4
1992	Fall	2	A	90	15	0.59	815.59	8059.5	1741.5	31.2
1993	Spring	1*	A	90	24	1.01	1625.28	17433.5	8608.5	91.2
1993	Spring	2	A	90	15	1.68	2229.7	15957.3	6127.8	59.8
1993	Fall	1	B	90	11	0.77	770.3	5500.0	5852.0	24.4
1993	Fall	2	B	90	23	0.58	1726.0	18673.2	10048.6	52.4
1994	Spring	1	B	90	19	0.92	1479.4	14462.8	6716.5	72.6
1994	Spring	2	B	90	21	0.95	1704.6	17469.9	9271.5	119.1
1995	Winter	Field	D	40-77	21	0.60	1511.8	11510.8	15799.0	71.3
1994	Fall	1	C	133	25	0.58	1930.1	17178.8	26194.0	67.6
1994	Fall	2	C	150	51	0.64	4863.0	34926.0	39634.3	129.8
1994	Fall	Field	D	133	28	0.60	2341.2	14473.6	20476.8	76.5

Ration: A=75:25 oats:barley blended & rolled + Fescue Straw
B=50:50 oats:barley blended & rolled + Barley Straw
C=Oats + Grass Hay
D=Start on Oats, then 75:25, then 50:50 + Grass Hay
*:some animals removed from trial early for marketing purposes

The total amount of grain consumed, forage consumed and mineral consumed per pen.

Table 6: Total average daily gain (kg) and average daily grain consumed (kg), average daily forage consumed (kg), average daily mineral consumed (kg) and average daily combined feed consumed (kg) per animal.

Year	Season	Pen	Ration	Days	# of Bulls	Total ADG	Avg. Daily Grain	Avg. Daily Forage	Avg. Daily Mineral	Avg. Daily Total Feed
1992	Fall	1	A	90	28	0.87	7.4	2.5	0.02	10.0
1992	Fall	2	A	90	15	0.59	6.0	1.3	0.02	7.2
1993	Spring	1*	A	90	24	1.01	8.1	3.9	0.04	16.0
1993	Spring	2	A	90	15	1.68	11.8	4.5	0.04	16.4
1993	Fall	1	B	90	11	0.77	5.6	5.9	0.03	11.5
1993	Fall	2	B	90	23	0.58	9.0	4.9	0.03	13.9
1994	Spring	1	B	90	19	0.92	8.5	3.9	0.04	12.4
1994	Spring	2	B	90	21	0.95	9.2	4.9	0.06	14.1

Ration: A=75:25 oats:barley blended & rolled + Fescue Straw
B=50:50 oats:barley blended & rolled + Barley Straw
*:some animals removed from trial early for marketing purposes

Bison tended to consume more total feed in the spring than in the fall. In the spring of 1993 bison consumed 16.0 – 16.4 kg. of total feed per animal daily, compared to 7.2 – 10.0 kg. of total feed per animal daily in the fall of 1992. In 1994, bison consumed 12.4 – 14.1 kg. of total feed per animal daily compared to 11.5 – 13.9 kg. of total feed per animal daily in the fall of 1993. Bison consumed more mineral daily (0.04 – 0.06 kg) in the spring than in the fall (0.02 – 0.03 kg.) There does appear to be higher average daily grain and forage consumption in the spring than in the fall. However, these trends are not significantly different (p<05), but the difference becomes significant when the two are combined.

Table 7a. Average daily grain consumed (kg) per animal by season.

	Count	Mean	Std. Dev.	Std. Error
Fall	4	6.989	1.570	.785
Spring	4	9.405	1.679	.840

Table 7b. Average daily forage consumed (kg) per animal by season.

	Count	Mean	Std. Dev.	Std. Error
Fall	4	3.650	2.110	1.055
Spring	4	4.318	.490	.245

Table 7c. Average daily combined feed consumed (kg) per animal by season.

	Count	Mean	Std. Dev.	Std. Error
Fall	4	10.639	2.771	1.386
Spring	4	14.723	1.835	.917

Table 8: Total average daily gain (kg) and total grain conversion (kg), total forage

Year	Season	Pen	Ration	Days	# of Bulls	Total ADG	Total Grain Feed Conv.	Total Forage Feed Conv.	Total Combined Feed Conv
1992	Fall	1	A	90	28	0.87	8.7	3.0	11.7
1992	Fall	2	A	90	15	0.59	9.9	2.1	12.0
1993	Spring	1*	A	90	24	1.01	10.7	5.3	16.0
1993	Spring	2	A	90	15	1.68	5.7	2.7	9.9
1993	Fall	1	B	90	11	0.77	6.4	7.6	14.7
1993	Fall	2	B	90	23	0.58	10.8	5.8	16.6
1994	Spring	1	B	90	19	0.92	9.8	4.5	14.3
1994	Spring	2	B	90	21	0.95	10.2	5.4	15.7
1995	Winter	Field	D	40-77	21	0.60	7.6	10.5	18.0
1994	Fall	1	C	133	25	0.58	8.9	13.6	22.5
1994	Fall	2	C	150	51	0.64	7.2	8.2	15.3
1994	Fall	Field	D	133	28	0.60	8.7	6.2	14.9

The total grain feed conversion per pen is similar between pens and between seasons. The total grain feed conversion per pen ranges from 7.2 to 10.8. The total forage feed conversion per pen and the total combined feed conversion per pen had a much broader range, from 2.1 to 13.6 and 9.9 to 22.5 respectively.

Table 9a. Means of total grain feed conversion (kg) by season.

	Count	Mean	Std. Dev.	Std. Error
Fall	4	8.920	1.929	.965
Spring	4	9.094	2.327	1.163

Table 9b. Means of total forage feed conversion (kg) by season.

	Count	Mean	Std. Dev.	Std. Error
Fall	4	4.633	2.529	1.264
Spring	4	4.507	1.237	.619

Table 9c. Means of total combined feed conversion (kg) by season.

	Count	Mean	Std. Dev.	Std. Error
Fall	4	13.760	2.364	1.182
Spring	4	13.977	2.812	1.406

None of the means in the above tables are significantly different (p<0.05). The total grain feed conversion (table 9a), total forage feed conversion (table 9b), and the total combined feed conversion (table 9c) are very similar between the fall and spring season.

Average daily gain was higher in experiment 1 when animals were fed a 75:25 ration with fescue straw compared to the following year when animals were fed a 50:50 ration with barley straw (figure 4). A 75:25 oats-barley ration and fescue straw may be more beneficial than a 50:50 ration and barley straw. Bulls on the 75:25 ration and fescue straw gained more (1.1 ± 0.04 kgd^-1 than bulls on the 50:50 ration and barley straw (0.78 ± 0.05 kgd^-1). However caution must be used in interpreting these numbers as the rations were fed in different years (experiment 1 and experiment 2) and may potentially be confounded by year .Further study is required to determine the effects of ration on average daily gain.

The ADG of one pen in the winter (Winter 1995, Field) was not significantly different from the ADG of the fall pens. This pen was composed of animals from many different herds and had different animals moving in and out of the pen at different times.

ADG of this pen is consistent with our previous unpublished observations.

In experiment 1, there was a significant pen by season interaction. Animals in Pen 2 gained significantly more (p<0.05) in the spring than in the fall, but there was no difference between the average daily gain in Pen 1 in the spring versus the fall (figure 5).

A similar interaction occurred during experiment 2, where animals in the spring gained significantly more during the first 45 days of the trial (ADGSM - 1.2 ± 0.06 kgd^-1 vs 0.6 ±0.07 kgd^-1) than in the fall. During the next 45 days, the ADG was not significantly different between animals in the spring and the fall (ADGME - 0.64 ± 0.06 vs 0.86 ± 0.06kgd^-1. Overall: ADG was greater in the spring than in the fall season (ADGSE - 0.94 ±0.04 vs 0.77 ± 0.05 kgd^-1) (figure 6). One potential explanation for this finding is that the animals in one pen (Pen 2) gained significantly more during Day 0 to Day 45 (ADGSM) than the animals in the other pen (pen 1) (figure 7). In experiment 2, animals in Pen 2 gained significantly more during the first 45 days of the trial (ADGSM - 1.1 kg vs 0.75 kgd^-1) than Pen 1, during the next 45 days the ADG was reversed with animals in Pen 1 gaining more than the animals in Pen 2 (ADGME - 0.90 ± 0.03 vs 0.60 ± 0.03 kgd^-1.There was no significant difference in the ADG in the two pens overall (ADGSE - 0.8 ± 0.06 kgd^-1).

A warm-up period was shown to be beneficial to average daily gain (figure 8). Bulls were placed in one of four classes depending on how long they were warmed up prior to Day 0 of the feedlot trial. Bulls that received no warm-up gained the least (0.86 ± 0.02 kgd^-1), bulls that were held between 6-20 and 20-50 days gained moderately more (1.1 ± 0.10 kgd^-1), and bulls that were held and fed a warm-up ration for more than 50 days had the greatest average daily gain (1.5 ± 0.07 kgd^-1).

Mixing small groups of bulls for the purpose of filling the pen was shown to be detrimental to average daily gain. The data were edited and records were excluded from the analysis if the pen consisted of bulls from one producer only because they were confounded with season; therefore, only pens with bulls from more than one producer were included in this analysis. Bulls within a pen, that were in a group consisting of four or more bulls from the same producer, gained significantly more (p <0.05) than bulls that were within a group from the same producer that was less than or equal to three bulls in size (0.68 ± 0.03 kgd^-1 vs 0.36 ± 0.4 kgd^-1) (table 9).

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Fig. 9

Discussion

While the popularity of bison meat with consumers, the number of bison on farms and the number of new bison farms starting up all continue to increase rapidly, there are surprisingly few studies in recent years regarding bison performance under either intensive farm or more extensive ranch conditions. This study has demonstrated that the effect of season is important when feedlot finishing young bison bulls on grain rations.

When bison are grain finished during the spring season as opposed to the fall season their ADG was significantly greater. This finding supports work done by Christopherson et al. (1977, 1979a, 1979b) that demonstrated that there is a seasonal effect on metabolic rate of bison. There may be some advantage gained by grain finishing bison in the spring as opposed to the fall season. However, the fact that the feed conversion ratio (grain, forage or combined) is nearly identical between seasons does serve to diminish the impact of the seasonal effect. The total feed conversion ratios and ADG in this study were similar to Rutley and Church (1995) and a smaller previous study (Koch et al. 1988) which compared the growth of 10 bison with 12 Hereford and 10 Brahman cattle (bison: 8.2 FCR food conversion ratio, 0.76 ADG kgd^-1). While the feed conversion ratio is higher in Koch et al (1988), they were fed a considerably different ration (66% maize silage, 22% maize and 12% soybean + mineral supplement). Rutley (1992a) reported grain conversions ranging from 7.78 to 13.42 for four groups of bison bulls fed equivalent rations to experiment 1.

Results from this study tend to contradict the finding that there may be a benefit in feeding a diet with slightly higher protein in the ration. However caution must be used when interpreting this data. While the ADG was higher in bison fed the 75:25 ration with fescue straw compared to bison fed the 50:50 ration and barley straw, the diets were fed in successive years, not concurrent years, and may potentially be confounded. What this data does demonstrate, is that more research is warranted to determine the effects of protein supplementation on the ADG of feedlot finished bison.

Bison tended to gain more in the spring, but they also had a higher average daily feed consumption, resulting in similar feed conversion ratios between seasons. Similar feed conversion between seasons contradicts the findings of Stanton et al (1995) in-groups of fed yearling bison bulls. Whether location (Colorado), ration (corn, cottonseed meal), age (yearling vs two year olds ), frequency of handling or some other unidentified factor could explain this difference is unknown. Further research would seem appropriate.

Since bison had a higher ADG in the spring compared to the fall season, this would, reduce the amount of time that the animals would have to spend in the feedlot, and would subsequently reduce cost of production (Hussey 1995).

Warm-up was demonstrated to be beneficial to ADG, suggesting that bison habituate to their surroundings and that it allows the rumen microorganisms time to adjust to grain as a source of nutrients. This data also suggests that the practice of slowly increasing the grain content of the ration may be of benefit. Even though bison can be placed on full feed directly with a minimum of problems, it doesn't necessarily mean placing bison on feed directly is optimal.

When bison bulls are mixed upon entering the feedlot for the purpose of filling the pen, it is beneficial to keep the number of head from the herd of origin as large as possible. Even a group size of four is preferable to a group size of three or less. Mixing unfamiliar animals is the major cause of dark cutting beef (DCB) in cattle. Mixing promotes homosexual and agonistic or aggressive behaviour, particularly in young bulls (Warris et al. 1984, Warris 1990). Handling practices which encourage mixing; therefore, increased the incidence of DCB, lower performance and increase stress (Jones and Tong 1989, Mench et al. 1990, Mohan et al. 1991, 1992). Although dark cutting does not appear to be a problem with bison (Rutley, unpublished data), mixing of unfamiliar bison bulls should be avoided as much as possible to reduce loss of ADG.

The second order interactions discovered between season and pen with regards to ADG in both experiment 1 and 2 suggest that the ADG of bison is sensitive and quite variable. These results suggest that efforts should be made to standardize facility and handling procedures with bison as much as possible to promote familiarity and consistent ADG.

Implications

Bison gain more when started on grain finishing in the spring compared to fall, but they also had higher average daily feed consumption. The resulting similar feed conversion ratios between seasons imply that there are no appreciable losses associated with lower winter feed conversions, which is a clear advantage for the bison industry .

Since bison have a higher ADG in the spring compared to the fall season, there would be a reduction in the amount of time that animals would have to spend in the feedlot in the Spring.

There is a benefit to a warm-up period prior to grain finishing. Even a period of six days was more beneficial compared to no warm-up.

When bison bulls are mixed upon entering the feedlot for the purposes of filling the pens, it is beneficial to keep the number of head from the herd of origin as large as possible. Even a group size of four is preferable to a group size of three or less.

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