Serving Capacity of Crossbred Yearling Beef Bulls. I. Single-Sire Mating Behavior and Fertility during Average and Heavy Mating Loads at Pasture

Abstract

Eighty crossbred, virgin, yearling beef bulls were subjected to three serving capacity (SC) tests. Ten low SC (LSC) and 10 high SC (HSC) bulls similar in weight (avg wt = 452 kg), testicular size and seminal traits but differing in average services were selected. Objectives were to evaluate the mating behavior and fertility of LSC and HSC bulls at pasture when exposed to an average and a heavy mating load and to determine the effect of sexual activity on body weight and testicular characteristics. One LSC and one HSC bull per block were exposed single-sire to 25 naturally cyclic (N) cows for 3 d and to 9 estrus-synchronized (S) cows for 1 d in a randomized complete block design consisting of 10, 4-d blocks. Bulls were fitted with pedometers to record distance travelled. Behavioral data were collected by periodic visual observation. During the N cow treatment, LSC bulls had fewer (P less than .05) services per cow, total services and a higher mount to service ratio than HSC bulls. During the S cow treatment, LSC bulls showed increased sexual activity, though they achieved fewer (P less than .09) services per cow. Pregnancy rates for LSC and HSC bulls did not differ (P greater than .20) and across SC groups averaged 53.6% for N cows and 31.9% for S cows. Distance travelled also was similar (P greater than .20) between SC groups for both treatments. Sexual activity during pasture exposure had no effect (P greater than .20) on testicular characteristics but resulted in an average decline in body weight of 25.7 kg across SC groups during the 4-d period. Post-exposure SC tests found that LSC bulls had increased (P less than .05) services, decreased mounts and mount to service ratio compared to pre-exposure measurements, but LSC were still lower (P = .06) than HSC bulls for average services. These results suggest that LSC virgin, yearling bulls should be offered sexual experience and retested before their inherent SC can be determined.

Study of correlation between reaction time and refractory period (as indices of libido) with semen characteristics in ArkharMerino×Moghani and Baluchi×Moghani rams

“…Some researchers claim that the relationship between measures of libido and fertility is inconspicuous. However, other reports showed positive (Crichton and Lishman, 1988;Blockey, 1989) or contradictory or negative correlations (Boyd et al, 1989;Bertram et al, 2002;Holroyd et al, 2002). Albeit, several Brazilian reports indicate no correlation between libido and seminal traits in Nellore bulls (Pineda et al,.…”

Fertility of yearling beef bulls during mating

“…Yearling beef bulls in groups of two, exposed to natural mating for 3 days, and estrussynchronized mating for 1 day, were evaluated for the effect of mating load on fertility [23]. On post-exposure observations, the bulls had body weight losses of 25-26 kg, with concurrent increases in scrotal circumference, however, seminal characteristics were not altered from pre-breeding BSE findings.…”

“…Variability in fertility of bulls with satisfactory potential-breeder classification on BSE has been reported [8,[23][24][25][26]. Bulls of diverse genotypes have had differences in physical and reproductive traits from 12 to 18 months of age and general improvements in fertility-potential through this period [10,27,28].…”

Causes of rejection of beef bulls in breeding soundness evaluation

“…On the other hand, evaluating bulls only as to libido and mounting capacity may lead to inaccurate conclusions, since factors related to the previous experiences of bulls may affect the results of the test (Boyd et al, 1989). Lopes et al (2009) considered that neither the andrological classification in scores nor the sexual behavior assessment were efficient to predict the breeding potential of Nellore bulls in terms of pregnancy rate at the end of the breeding season.…”