Researchers have contributed by increasing our understanding of the factors affecting reproduction in beef, mainly physical health and nutrition aspects, which have been main concerns during decades. Animal welfare is of outmost relevance in all animal production systems and it is strongly associated to stress. Stress responses involve endocrine, paracrine and neural systems and the consequences of this stress on the reproductive efficiency of specifically, beef cattle and bulls, need to be highlighted. We, therefore, describe the fundamentals of stress and its quantification, focusing in beef herds, reviewing the highly valuable pieces of research, already implemented in this field. We examine major factors (stressors) contributing to stress in beef cattle and their effects on the animals, their reproductive performance and the success of reproductive biotechnologies. We include terms such as acclimatization, acclimation or temperament, very relevant in beef systems. We examine specifically the management stress due to handling, social environment and hierarchy or weaning effects; nutritional stress; and thermal stress (not only heat stress) and also review the influence of these stressors on reproductive performance and effectiveness of reproductive biotechnologies in beef herds. A final message on the attention that should be devoted to these factors is highlighted.

A blinded, negative controlled, randomized intervention study was undertaken to test the hypothesis that addition of meloxicam, a nonsteroidal anti-inflammatory drug, to antimicrobial treatment of mild to moderate clinical mastitis would improve fertility and reduce the risk of removal from the herd. Cows (n=509) from 61 herds in 8 regions (sites) in 6 European countries were enrolled. Following herd-owner diagnosis of mild to moderate clinical mastitis within the first 120 d of lactation in a single gland, the rectal temperature, milk appearance, and California Mastitis Test score were assessed. Cows were randomly assigned within each site to be treated either with meloxicam or a placebo (control). All cows were additionally treated with 1 to 4 intramammary infusions of cephalexin and kanamycin at 24-h intervals. Prior to treatment and at 14 and 21 d posttreatment, milk samples were collected for bacteriology and somatic cell count. Cows were bred by artificial insemination and pregnancy status was subsequently defined. General estimating equations were used to determine the effect of treatment (meloxicam versus control) on bacteriological cure, somatic cell count, the probability of being inseminated by 21 d after the voluntary waiting period, the probability of conception to first artificial insemination, the number of artificial insemination/conception, the probability of pregnancy by 120 or 200 d postcalving, and the risk of removal by 300 d after treatment. Cox's proportional hazards models were used to test the effect of treatment on the calving to first insemination and calving to conception intervals. Groups did not differ in terms of age, clot score, California Mastitis Test score, rectal temperature, number of antimicrobial treatments given or bacteria present at the time of enrollment, but cows treated with meloxicam had greater days in milk at enrollment. Cows treated with meloxicam had a higher bacteriological cure proportion than those treated with the placebo [0.66 (standard error=0.04) versus 0.50 (standard error=0.06), respectively], although the proportion of glands from which no bacteria were isolated posttreatment did not differ between groups. No difference was observed in the somatic cell count between groups pre- or posttreatment. The proportion of cows that underwent artificial insemination by 21 d after the voluntary waiting period was unaffected by treatment. Treatment with meloxicam was associated with a higher proportion of cows conceiving to their first artificial insemination (0.31 versus 0.21), and a higher proportion of meloxicam-treated cows were pregnant by 120 d after calving (0.40 versus 0.31). The number of artificial inseminations required to achieve conception was lower in the meloxicam compared with control cows (2.43 versus 2.92). No difference was observed between groups in the proportion of cows pregnant by 200 d after calving or in the proportion of cows that were culled, died, or sold by 300 d after calving (17% versus 21% for meloxicam versus control, respectively). ...

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