Can we build the cowherd by increasing longevity of females?

Authors: Roberts, Andrew; Petersen, Mark; FUNSTON, RICHARD - University Of Nebraska

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2015
Publication Date: 4/1/2015
Citation: Roberts, A.J., Petersen, M.K., Funston, R.N. 2015. Can we build the cowherd by increasing longevity of females? Journal of Animal Science. 93:4235-4243.

Interpretive Summary: Increasing longevity of beef cows by decreasing proportion culled due to reproductive failure provides an efficient process to rebuild a cow herd and can reduce number of replacements needed to sustain a constant herd size. Rate of reproductive failure varies due to cow age, where failure in 2 to 4 year old cows is often greater 5 to 7 year old cows. In addition, weight of cow and calf at weaning increase as cows advance from 2 to 5 years of age. The cumulative effect of increasing retention of young cows is improved production efficiency through decreased replacement rate and changing age structure of the herd resulting in a greater proportion of cows at maximal production potential for weight of calf at weaning and cow at time of culling. Calculations from cow age specific culling and BW data from commercial and research herds indicates reducing replacement rate from 18 to 14% can result in 23% increase in calf weight weaned and 2 % increase in cull cow weight per pregnant replacement heifer going into the herd. Although improving longevity has huge potential, genetic advancement in sustained reproductive function is challenging, as it is the sequential culmination of the annual repetition of numerous discrete physiological processes, each ending in a qualitative response. Successful completion of one process is prerequisite to evaluate subsequent processes. These physiological processes are subject to nutritional threshold requirements that may vary due to genetic potential for other production traits such as milk, growth and mature size resulting in genetic x nutrition interactions. This is in contrast to most traits for which EPDs exist, where genetic by environmental interactions are not considered to be substantial. Extensive research concerning impact of limited nutrition on reproduction has led to recommendations that heifers and cows be fed to a threshold weight or condition score to ensure reproductive success; a process that masks nutritional interactions that might otherwise result in reproductive failure. This management approach minimizes selection for animals capable of sustained reproductive function under limited nutritional environments. Rearing and managing cows under nutritionally limited environments may lead to adaptation to relatively high levels of reproductive success under lower input levels. Such adaptation may improve chances for longer retention in their offspring in nutrient limited environments.

Technical Abstract: Increasing longevity of beef cows by decreasing proportion culled due to reproductive failure provides an efficient process to rebuild a cow herd and can reduce number of replacements needed to sustain a constant herd size. Rate of reproductive failure varies due to cow age, where failure in cows 2 to 4 yr of age is often greater than in cows 5 to 7 yr of age. In addition, BW of cow and calf at weaning increase as cows advance from 2 to 5 yr of age. The cumulative effect of increasing retention of young cows is improved production efficiency through decreased replacement rate and changing age structure of the herd resulting in a greater proportion of cows at maximal production potential for calf BW at weaning and cow BW at time of culling. Calculations from cow age specific culling and BW data from commercial and research herds indicates reducing replacement rate from 18 to 14% can result in 23% increase in calf BW weaned and 2 % increase in cull cow BW per pregnant replacement heifer going into the herd. Although improving longevity has huge potential, genetic advancement in sustained reproductive function is challenging, as it is the sequential culmination of the annual repetition of numerous discrete physiological processes, each ending in a qualitative response. Successful completion of one process is prerequisite to evaluate subsequent processes. These physiological processes are subject to nutritional threshold requirements that may vary due to genetic potential for other production traits such as milk, growth and mature size resulting in genetic x nutrition interactions. This is in contrast to most traits for which EPDs exist, where genetic x environmental interactions are not considered to be substantial. Extensive research concerning impact of limited nutrition on reproduction has led to recommendations that heifers and cows be fed to a threshold BW or BCS to ensure reproductive success; a process that masks nutritional interactions that might otherwise result in reproductive failure. This management approach minimizes selection for animals capable of sustained reproductive function under limited nutritional environments. Rearing and managing cows under nutritionally limited environments may lead to adaptation to relatively high levels of reproductive success under lower input levels. Such adaptation may improve chances for longer retention in their offspring in nutrient limited environments.