Preventive Veterinary Medicine, 18 (1994) 99-113 99 Elsevier Science Publishers B.V., Amsterdam

Health and productivity of beef breeding bulls in Ontario

John J. McDermott a,*, S. Wayne Martin a, O. Brian Allen b "Department of Population Medicine, University of Guelph, Guelph, Ont. NIG 2W1, Canada

bDepartment of Animal and Poultry Science, University of Guelph, Guelph, Ont. NIG 2W1, Canada

(Accepted 23 April 1993)

Abstract

One hundred and seventy-eight randomly selected Ontario cow-calf herds were followed from breeding in 1986 to calving in 1987. The distributions of age, breed, culling, and disease for 315 breeding bulls and the patterns of bull management and usage in these herds are described. Potential associations between individual bull factors and bull fertility were examined for a subset of 134 bulls, from 106 herds, used in single-sire breeding groups.

Limousin was the predominant bull breed. Hereford, Charolais and Simmental were also common. Lameness, both acute (6%) and chronic (5.7%), was the most frequently occurring disease class. Other diseases were recorded infrequently.

The average sire age was 3 years. The overall culling rate was 26. I% and age-specific culling rates increased with age. Prebreeding soundness examinations were used rarely. Of the 315 bulls followed, 134 had been enroled in official growth-performance tests.

The mean pregnancy rate in the 134 single-sire breeding groups was 92.7% and the mean group calving interval was 364.7 days (SD = 13.2 ). Chronic disease and supplemental grain feeding of bulls at selected periods in the year were associated with lower pregnancy rate. Both acute and chronic diseases of bulls were associated with increased mean group calving interval. Our analysis suggests that reproductive performance could be improved by better observation and replacement of diseased bulls just prior to and during the breeding season.

Introduction

The overwhelming majority of cows and heifers on Ontario cow-calf farms are bred by natural service (McDermott et al., 1991 ). Thus, the health and productivity of herd sires are crucial to the annual success of the cow-calf operation. The importance of bull selection and management for Ontario producers has been stressed (Field, 1985 ) and important selection and advi- sory programs funded by the Provincial Ministry of Agriculture and Food. However, little is known about the actual population of beef breeding bulls for Ontario cow-calf herds and how producers manage these bulls.

*Corresponding author.

© 1994 Elsevier Science Publishers B.V. All rights reserved 0167-5877/94/$07.00 SSDIO 167-5877 (93) 00279-E

100 Z,L McDermott et al. /Preventive Veterinary Medicine 18 (1994) 99-113

In this paper we will describe the distributions of age, breed, culling, dis- ease, and other characteristics for individual breeding bulls used for natural service on Ontario cow-calf farms in 1986. As well, potential associations be- tween bull fertility and individual bull factors will be examined using statis- tical models. At the herd level, patterns of bull management and usage will be described.

Materials and methods

Study population and data collection

The study population consisted of 315 bulls from 178 randomly selected cow-calf herds using at least one breeding bull in 1986. The sampling frame was a list of 1444 beef breeding herds with at least 25 cows, participating in a voluntary government-sponsored beef herd improvement program (BHIP) (estimated to be greater than 50% of all such herds). Study herds were se- lected via computer-generated random numbers after stratifying by region of Ontario. Further details on the study methods and herd descriptions have been published previously (McDermott et al., 1991 ).

Data on feeding, housing, management, and diseases, as well as individual- bull data on age, breed, breeding soundness examination, performance test- ing status, and breeding experience were collected from herd records and pro- ducer interviews by three investigators (McDermott et al., 1991 ). Addi- tional, more detailed data (including postweaning gain, end of test weight, hip height, backfat thickness and scrotal circumference) were accessed for a subset of 134 bulls from 106 herds tested under the Canadian Record of Per- formance (ROP) and Ontario Bull Test programs, which could be traced to specific breeding groups. (In Ontario, potential breeding bulls are trans- ported to designated facilities at 6-7 months of age to be performance tested. After an initial 1 month adjustment period, weight gain is measured over the next 140 day period. Hip height, backfat thickness and scrotal circumference are measured at the end of the testing period (Hamilton and Pogue, 1986 ). )

Bull fertility measures

Bull fertility was measured by the pregnancy rate and the mean calving in- terval ( 1986-1987 calving) of females bred by that bull. Pregnancy status of cows and heifers bred by approximately 30% of these bulls was determined by rectal palpation. For the cows and heifers bred by the remaining bulls, pregnancy status was estimated, based on the following classification system: ( 1 ) pregnant, if they subsequently calved, aborted, or were sold as breeding stock; (2) open, if they were culled by the farmer as open, retained open through the next calving season, or culled for no specific cause more than 11

J.J. McDermott et al. / Preventive Veterinary Medicine 18 (1994) 99-113 101

months after the last calving; (3) unknown, if they died prior to calving, were culled for a specific cause other than non-pregnancy or were culled for no specific cause within 11 months of the last calving.

Mean calving interval for females bred by a bull is the arithmetic mean of individual calving intervals for females calving in both 1986 and 1987.

Statistical analysis

Associations between age class and the occurrence of either disease or cull- ing for all bulls were assessed for both linear trend (Breslow and Day, 1987) and common odds ratios (Breslow and Day, 1980) in EGRET (Statistics and Epidemiology Research Corporation, Seattle, WA). Mean postweaning per- formance test results for study bulls, by breed, were compared with 1985- 1986 Ontario breed means using t-tests (Armitage and Berry, 1987).

The pregnancy rate for groups of females bred by the 134 tested sires was modelled as a binomial outcome by logistic regression using two statistical packages: EGRET and GLIM (Numerical Algorithms Group, Oxford, UK). Pregnancy check status, length of breeding season, and main breeding season (see Table 1 ) were forced into each model. Additional bull variables (see Table 1 ) were selected sequentially based on the most significant score tests (Pregibon, 1982) until no further variables had a significant score test (P> 0.05 ). Three first-order interaction variables (Table 1 ), to test specific hypotheses regarding the interrelationships of age, number of females bred, breed and grain feeding, were also specifically examined for model inclusion. Each variable in the final model was checked for significance using a likeli- hood-ratio test (reductions in deviance) (McCullagh and Nelder, 1989, pp. 118-119).

Two potential statistical problems with the above model are that not all sires or breeding females within sires were independent (56 bulls had at least one other bull herdmate in the model) and that no variables associated with the breeding females were included. To overcome these, the logistic regres- sion models were extended with an overdispersion parameter, estimated us- ing logistic normal regression (Pierce and Sands, 1975 ) in EGRET, and by a quasi-likelihood approach (Wedderburn, 1974) in GLIM.

Mean calving interval for females bred by the 134 tested sires was modelled using the weighted least-squares regression package BMDP-2R (BMDP Sta- tistical Software, Los Angeles, CA). Each observation was weighted by the number of animals contributing calving interval data. The interval between first calving dates in 1986 and 1987 was forced into the mean calving interval model to control for variations in time from calving to bull exposure.

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Table 1 Variables examined for associations with pregnancy rate and mean calving interval in specific sire breeding groups, 1986-1987

Forced variables Pregnancy check status (rectal palpation (yes/no) ) Length of breeding season (number of days in which 90% of females calved (mean = 87.8; SD=53.7)) Main breeding season (fall-winter (Oct.-Mar.), spring (Apr.-May), early summer (June), late summer (July-Sep.) )

Main effect variable Bred cows in another herd (yes/no) Breeding soundness exam by a veterinarian before the bull was purchased (yes/no) Supplemental grain fed ~ (all year/selected periods/never) Performance tested (yes/no) Age class (yearling, 2 year-first breeding season, 2 year-second breeding season, 3 year, 4 year, ( 5 year or more) Short duration ( < 2 weeks) disease during breeding season (yes/no) Chronic ( >t 2 weeks) disease during breeding season (yes/no) Heifers bred (none/< 50%/> = 50%) Bull housed separately during the non-breeding season (yes/no) Artificial insemination also used (no/selected animals/majority) Breed (Hereford, Limousin, Charolais, Simmental, other)

Interaction variables Age class and supplemental grain feeding Age class and number bred Breed and supplemental grain feeding

~Supplemental grain feeding reported by the producer; amounts not specified.

Results

Descriptive statistics on the 315 bulls are presented in Table 2. Limousin was the predominant bull breed. Individual-sire fertility outcomes could be determined for 134 of the 315 bulls.

Lameness, both acute ( < 2 weeks duration) and chronic, was the most fre- quently occurring disease class reported by producers. Other diseases were recorded infrequently. Diseases of short duration ( < 2 weeks) occurred with the same frequency in all age classes (test for common odds ratio, P = 0.71 ), while chronic diseases were more frequent in older bulls (Table 3) (exact trend test, (Breslow and Day, 1987 ), one-sided P = 0.02).

Of the bulls in their first breeding season, two-thirds were yearlings and the other third were 2 years of age. The number of bulls in each age class de- creased with increasing age (Table 3 ). This trend was mirrored by an increas- ing age-specific culling rate (Table 3) (exact trend test, EGRET, one-sided P=0.001 ).

Prepurchase breeding soundness examinations were used rarely in selecting

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Table 2 Descriptive statistics of the 315 bulls used for breeding in 1986 on 178 randomly selected Ontario cow-calf herds using natural service

Variable Number Percentage

B r e e d

Angus 21 6.7 Charolais 59 18.7 Hereford 67 21.3 Limousin 91 28.9 Simmental 50 15.9 Other 27 8.6

Bred cows in other herds I 39 12.4

Breeding soundness exam 2 9 2.9

Performance tested 134 42.5

D i s e a s e s 3

Acute lameness 4 19 6.0 Chronic lameness 4 18 5.7 Digestive 4 1.3 Eye 4 1.3 Reproductive 6 1.9 Respiratory 2 0.6 Other 2 0.6

qn 1986. 2Prepurchase or prebreeding season. 3Diseases were those observed and diagnosed by the farmer with or without veterinary assistance. 4Acute was less than 2 weeks duration, otherwise chronic.

Table 3 Age distribution and age-specific culling and disease rates for 315 bulls used for breeding in 1986 on 178 randomly selected Ontario cow-calf herds using natural service

Age class Number of Culling rate ~ Disease rate (year) bulls (%)

Short duration 2 Chronic 3

1 60 10.0 6.7 3.3 2-first 4 30 20.0 13.3 2.5 2-second 5 45 26.7 8.9 2.2 3 60 28.3 15.0 6.7 4 45 35.6 4.4 8.9 5 25 28.0 8.0 12.0 6 21 23.8 9.5 23.8 7 17 41.2 5.9 11.8 />8 12 50.0 8.3 8.3

Total 315 26.1 8.9 8.3

1Increasing age-specific culling rate (exact trend test, p=0.001 ). 2No association between short duration ( < 2 weeks) disease and age class (test for common odds ratio, p = 0.71 ). 3Increasing age-specific chronic ( >/2 weeks ) disease rate (exact trend test, p = 0.02 ). 4First breeding season. ~Second breeding season.

104 J.J. McDermott et al. /Preventive Veterinary Medicine 18 (1994) 99-113

Table 4 Postweaning performance-test results for the 134 previously performance tested bulls that bred cows on 178 Ontario cow-calf herds, in 1986

Breed Number Percentage Index 2 End of test Scrotal Backfat tested 1 weight circumference (mm)

(lb) (cm)

Angus 4 19.0 115.0"* 1157 34.3 4.5 (5.0) 3 (63.2) (1.5) (n.d.)

Charolais 24 40.7 123.9"* 1266"* 35.1"* 3.0 (2.0) (26.9) (0.7) (0.3)

Hereford 16 23.9 106.8 1112** 33.7* 6.7 (2.7) (36.0) (0.7) (0.6)

Limousin 52 57.1 112.6'* 1129 32.1"* 3.2 (3.0) (14.8) (0.4) (0.2)

Simmental 30 60.0 121.4 1302 36.4 4.5 (2.7) (27.9) (0.4) (0.3)

Other 8 29.6 124.1 1276 35.3 4.2 (6.1) (38.8) (1.5) (0.9)

Total 134 42.5 116.7 1198 34.0 4.0 (1.5) (13.1) (0.3) (0.2)

1percentage of bulls tested from total number of bulls used in study herds. 21ndex of weight gain during test period compared with other bulls in the same test group. See Ham- ilton and Pogue (1986) for details. 3 ( ), Standard deviation. **Significantly (t-test, P< 0.05) greater than means for all bulls of the same breed tested in Ontario during 1985-1986 (McMorris et al., 1988, p. 10). n.d., not done.

bulls (Table 2). However, Hereford, Charolais and Limousin bulls selected from the testing program had higher than average scrotal circumferences, as well as a higher than average rate of gain and/or end of test weights for their breed (Table 4).

Of the 97 herds with more than one bull, 78 (80.4%) split the herd into breeding groups bred by a single sire. Separate housing for bulls during the non-breeding season was provided in just over half (54.5%) of herds (Table 5 ). Supplemental grain feeding was common in the prebreeding season, but infrequent during the breeding season.

Pregnancy rates for the 134 single-sire breeding groups were high (Fig. 1 ). The logistic and the quasi-likelihood models of pregnancy rate are displayed in Table 6. The other model examined (the logistic-normal) was very similar to the quasi-likelihood model. The logistic regression model fit the data poorly. The observed Pearson statistic of 244.9 was well above the expected value of 118 (McCullagh and Nelder, 1989).Despite this poor fit, however, the logis-

J.Z McDermott et al. / Preventive Veterinary Medicine 18 (1994) 99-113 105

Table 5 Patterns of bull management and bull usage in 178 randomly selected Ontario cow-calf herds using natural service

Number Mean or percentage

Type of breeding Majority AI 7 3.9 Some AI 27 15.2 Entirely natural service 144 80.9

Breeding experience of bull(s) All inexperienced 27 15.2 All experienced 96 53.9 Combination 55 30.9

Number of sires per group Single 159 89.3 Multiple 19 10.7

Bulls housed when not breeding Separate from cows 97 54.5 Remain with cows 81 45.5

C o w : bull ratio 29.3 (27.6, 31.0) t

Grain feeding Prebreeding2: selected bulls 13 7.3

all bulls 114 64.0 Breeding: selected bulls 4 2.2

all bulls 16 9.0 Non-breeding: selected bulls 13 7.3

all bulls 88 49.4

' Ninety-five per cent confidence interval for mean cow: bull ratio. 2Prebreeding is the 2 month period prior to breeding.

tic and quasi-likelihood models (inflated to account for such poor fit) were very similar.

Of the forced variables, main breeding season was associated with preg- nancy rate in all models; pregnancy rates were lowest in groups bred in the spring and early summer. The surrogate measure of breeding season length (the period in which 90% of females calved) was quite long in most study herds: less than 6 weeks in 16% of herds; 6 to less than 9 weeks in 28% of herds; 9 to less than 12 weeks in 16% of herds; 12 to less than 15 weeks in 10% of herds; and more than 15 weeks in the other 30% of herds. Pregnancy

106 J.J. McDermott et al. / Preventive Veterinary Medicine 18 (1994) 99-113

50

40

CO 0..

0 30 03

o

o3

c'- ~ 2O

O .

10

<70 70 73 76 79 82 85 88 91 94 97 100

group pregnancy rate (%)

Fig. 1. Distribution of group pregnancy rate for 134 specific sire breeding groups, 1986.

rates were not associated with either breeding season length or with the use of pregnancy examinations.

Of the variables offered for selection, chronic bull disease and supplemen- tal grain feeding were associated with pregnancy rate in all models (Table 6 ). Bulls suffering from chronic diseases had lower pregnancy rates (e.g. a 3% decrease for a bull having all the baseline categories; quasi-likelihood model ). Bulls fed supplemental grain during selected periods (usually in the 2 months prior to breeding) had lower pregnancy rates than bulls fed either no grain, or those fed grain throughout the year. This relationship held true across all age classes. )

The distribution of mean group calving interval is displayed in Fig. 2 and the statistical model selected is presented in Table 7. Interval between first calving dates in 1986 and 1987 (a surrogate measure to adjust for planned or actual delays in the beginning of the 1986 breeding season relative to 1985 ) had the most significant association with calving interval. Each 1 day increase in the interval between first calving dates for years 1986 and 1987 increased

J.Z McDermott et al. /Preventive Veterinary Medicine 18 (1994) 99-113 107

Table 6

Models of pregnancy rate for 134 specific sire breeding groups in 106 Ontario cow-calf herds, 1986 breeding season

Variable Logistic model (in order of entry)

Quasi-likelihood model

b 1 P-value b I P-value

Intercept 5.05 3.85 Overdispersion parameter 1.942 < 0.01

Forced variables

Pregnancy check

Breeding season length

Breeding season Spring - 0.89 Early summer - 1.10 Late summer (vs. fall- -0 .11 winter)

Selected variables

Bull chronic disease - 0.66

Supplemental grain Selected period only - 0.87 All year (vs. no grain) -0 .01

Age class 2 year ( 1st season) - 0 . 8 0 2 year (2nd season) -0 .63 3 year -0 .61 4 year - 1.23 /> 5 year - 1.01

Heifers bred

< 50% - 0.54 t> 50% (vs. none) -0 .49

-0 .07 0.65 0.07 0.73

-0 .00 0.17 -0 .00 0.10

<0.01 <0.01 -0 .86 -0 .92 -0 .11

<0.01 - 0 . 9 0 <0.01

<0.01 <0.01 -0 .78

0.02

< 0 . 0 1 - 0 . 1 3

<0.01 0.09

~Coefficients only reported for variables in the final model; variables with m classes have m - 1 indi- cator variables, coded yes= 1 and no=0. 2Versus a null value of 1. See McCullagh and Nelder ( 1989, pp. 124-128).

the 1986-1987 mean group calving interval by 0.4 days. Both acute and chronic bull disease increased the calving interval by approximately 9 days.

Owing to the small number of performance-tested yearling sires for which

1 0 8

20 I

J.J. McDermott et al, / Preventive Veterinary Medicine 18 (1994) 99-113

I [

15

if) C L

£ tD~

O 10

03

r 12o

Q_

0 i l u t m t m m ~ ~

322 332 342 352 362 372 382 392 402 412 422

group calving interval (days)

Fig. 2. Distr ibution of mean group calving interval for 134 specific sire breeding groups, calving season 1986 to calving season 1987.

Table 7 Model of mean calving interval of 134 specific sire breeding groups in 106 Ontario cow-calf herds, 1986 breeding season

Variable b SE (b) P-value Multiple (in order of entry ) (days) (final) R 2

Intercept 222.52

Interval between 1 st ~ calving 0.39 0.08 < 0.01 0.19 dates 1986-1987

Length of breeding ~ season 0.04 0.02 0.08 0.23 (days)

Breeding season ~ 0.14 0.28 Spring - 8.56 4.43 Early summer - 7.54 4.17 Late summer (vs. fall- - 3.52 4.44 winter)

Bull acute disease 8.65 3.40 0.01 0.32

Bull chronic disease 8.83 4.21 0.03 0.35

~These variables were forced into the model prior to the entry of other variables.

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we had reproductive outcomes (n = 29) no pregnancy rate or calving interval models were fit for this group.

Discussion

The actual bull management procedures followed on Ontario cow-calf farms may differ from practices recommended by veterinarians and animal scien- tists. Three particular comparisons were notable. One recommendation is to 'avoid using several bulls in one pasture' (Field, 1985 ). Eighty per cent of producers using multiple sires divided their herds into single-sire breeding groups. However, a more expensive recommendation, that of providing sep- arate housing for bulls during the non-breeding season (Field, 1985), was followed less commonly. Almost half (45.5% ) of producers left the bulls with the cows during the non-breeding season.

Breeding soundness evaluations are recommended (Murray, 1974; Elmore et al., 1975). However, only nine of 315 bulls (2.9%) were examined for breeding soundness at any time. Three contributing factors to this low per- centage may be the lack of veterinarians competent in evaluating breeding soundness, the comparatively confined breeding conditions in Ontario (vs. more extensive western Canadian conditions ) and the low (or perceived low) incidence of disorders solely identified by breeding soundness evaluations. McMorris et al. (1988) (based on responses from Ontario bull buyers) re- ported that 54.5% "expressed interest in having a breeding soundness evalu- ation performed", indicating a potential market for this service. However, the extra proportion of infertile bulls that routine breeding soundness examina- tions might i d e n t i f y - beyond scrotal circumference (routinely measured on all tested bulls ) and the careful observation of breeding performance D may be small. Makarechian and Farid (1985 ) point out that the controversy re- garding the potential effectiveness of breeding soundness evaluations is pri- marily fuelled by the small size of most studies. Breeding soundness exami- nations (including sperm evaluation (Wiltbank and Parish, 1986 ) and serving capacity tests (Blockey, 1978) ) provide extra information regarding breed- ing fitness. But, data from mandatory bull licensing in the UK indicated that only 1.7% of bulls examined in 1974 failed a breeding soundness examination (British Veterinary Association, 1975 ). Farmers' organizations argued that this represented an insufficient and uneconomic selection procedure.

Many factors may influence the age and culling patterns seen. A major fac- tor, given the small herd sizes, is to prevent bulls from breeding their own daughters. In single-sire herds, the average bull age was 2.34 (SE = 0.18 ) years if at least 10% of the breeding females were heifers and 3.74 (SE=0.21 ) years if less than 10% were heifers. There may also have been deliberate selection of younger bulls for faster genetic progress and/or handling ease.

Given the reliance on younger bulls, sire selection has both short- and me-

1 10 J..~ McDermott et al. / Preventive Veterinary Medicine 18 (1994) 99-113

dium-term consequences. Our data indicate that producers are selecting tested bulls with greater than average rate of gain and scrotal circumference. Some producers (particularly owners of British breeds) have criticized the Ontario bull test program, for overfeeding bulls to an extent that they are unsuitable for breeding as yearlings (McMorris et al., 1988 ). Our data indicate that pro- ducers did not delay using British breed bulls. Herefords (and also Charolais ) were more likely to be used as yearlings compared with Limousins and Sim- mentals. A similar breed trend for the interval from purchase to breeding for yearling bulls was found by McMorris et al. ( 1988 ).

The experimental evidence of potential reproductive problems in ad libi- tum fed tested bulls is not consistent. Coulter et al. ( 1987 ) reported negative effects on sperm production, Morrow et al. ( 1981 ) noted a tendency for bulls fed lower energy rations to rate higher in libido. On the other hand, Pruitt and Corah ( 1985 ) found no differences in serving capacity or semen evaluation between 29 Hereford and 27 Simmental bulls divided into low-, medium- and high-energy ration treatments, although all bulls had relatively poor semen quality. Since the interactions of age, breed and grain feeding were of interest to Ontario producers, the first-order interactions between these variables were estimated. None were significant, but with only 29 yearlings with specific re- productive outcomes our analyses have low power. McMorris et al. ( 1988 ) had concluded that the Ontario test station program has no practical detri- mental effect on reproductive performance. However, that study (McMorris et al., 1988 ) had a response rate of only 40%; so that the question of overfeed- ing young British breed bulls has not been convincingly resolved.

The overall reproductive performance of bulls in the study was, on the sur- face, excellent; only seven of the 134 specific sire breeding groups had preg- nancy rates of less than 80% and only ten groups had mean calving intervals of greater than 380 days. It is arguable that the high overall level of reproduc- tive performance was due to long breeding seasons and modest bull:cow ra- tios (McDermott et al., 1994 ). However, in the breeding groups studied, there was no association between breeding season length and pregnancy rate. This is a surprising result - - indicating perhaps that the effects of (relatively) re- stricted breeding season length were confounded by other factors (superior management perhaps).

The major objective in the reproductive performance models was to inves- tigate individual-bull factors associated with reproductive outcomes. A num- ber of potentially confounding factors were controlled, including: main breeding season, length of breeding season, herd pregnancy check status (in pregnancy rate models), and interval from first calving dates in 1986 and 1987 (in calving interval models). Other factors (particularly breeding fe- male management factors) were not formally controlled, since this informa- tion had been collected at the herd rather than at the specific sire breeding group level. To account for the presumed absence (due to these unexamined

J.J. McDermott et aL / Preventive Veterinary Medicine 18 (1994) 99-113 113

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