Original article by S.L. Lake, R. Arias, P. Gunn, and G.A. Bridges, from 2013 Range Beef Cow Symposium
Nutrition During the 21 Days Post Breeding: Maternal recognition of pregnancy takes place around day15-17 post-insemination and that transporting animals near this time compromises conception. However, moving heifers within the first 5 days post-insemination does not cause this reduction. Although, research suggests that conception rates are compromised when heifers are placed on early growth pasture forages. Researchers hypothesized that feeding this high moisture pasture forage at turnout is limiting dry matter intake which in turn causes a temporary energy deficiency that results in temporary heifer weight loss during the critical stages of early embryonic development and maternal recognition of pregnancy. Therefore, it is beneficial to ensure heifers maintain the same plane of nutrition after breeding, at least until day 25 when the embryo should be completely attached to the uterus. If this is true, maintaining a positive plane of nutrition on heifers after breeding will increase 1st service conception rates, improving herd fertility and longevity.
Some spring-born heifers are developed from weaning to breeding in a dry-lot pens. Estrous synchronization and AI may be conducted while in the dry-lot to take advantage of proximity to corral/breeding facilities. Following AI, heifers are may be moved to pastures to expose them to clean-up bulls. The researches hypnotized (Lake et al. 2013) this shift in diet quality and quantity of nutrients, may negatively impact metabolism, body weight gains, and ultimately reproductive efficiency.
Investigators at Purdue University and the University of Wyoming jointly examined the role of post-insemination nutrition on AI pregnancy rates in beef t two locations (Purdue; n = 53, Wyoming; n = 99) heifers were fed at 125% of NRC maintenance requirements (approximate ADG of 1.5 lbs/d) from weaning until estrous synchronization and AI. Immediately following estrous synchronization and AI, feed delivery to heifers was tightly controlled as heifers were specifically fed diets formulated to:
1) 125% of maintenance requirements
2) 100% of maintenance requirements
or 3) 80% of maintenance requirements
Heifers remained on these diets for 21 days following AI. Heifers that returned to estrus during the 21-day dietary treatment were inseminated and following the conclusion of the dietary treatment all heifers were comingled and placed with fertile bulls. Pregnancy diagnosis was conducted at 30 days post-AI to determine pregnancy success following the initial AI and 30 days after the breeding season to determine 2nd service AI pregnancy rates and overall breeding season pregnancy rates.