15 July 2014

4 minute read

Maternal recognition of pregnancy takes place around day 15-17 post-insemination and that transporting animals near this time compromises conception, writes Ohio State University extension beef specialist Steve Boyles, summarising a presentation by S.L. Lake, R. Arias, P. Gunn, and G.A. Bridges.

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 per cent 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 per cent of maintenance requirements
2) 100 per cent of maintenance requirements
3) 80 per cent 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.

Analyses revealed that heifers that were fed to continue their pre-breeding plane of nutrition (125 per cent maintenance) for 21 days post-AI had greater (P = 0.04) AI pregnancy rates compared to both groups of heifers that had a decrease in dietary plane of nutrition (100 per cent maintenance and 80 per cent maintenance). In addition, heifers in the 100 per cent NRC and 80 per cent treatments had decreased (P < 0.05) 2nd service AI pregnancy rates and decreased (P < 0.05) overall breeding season pregnancy rates.

If heifers are transitioned to pasture immediately following AI are supplemented with a concentrated feedstuff such as distillers grains to prevent post-AI weight loss, pregnancy rates are not negatively impacted.

Embryo Quality: It was hypothesized that day 6 embryos collected from heifers that were fed restricted, sub-maintenance diets would have poor embryo quality. This study was conducted at the University of Minnesota and South Dakota State University (SDSU). All heifers were on a common diet during development. Estrus was synchronized and timed-AI was conducted. On the day of AI, heifers were placed in one of two nutritional treatments:

At UMN

1) 120 per cent maintenance requirements
2) 80 per cent maintenance requirements

At SDSU

1) 125 per cent maintenance requirements

2) 50 per cent maintenance requirements

Dietary treatments were fed until embryo collection was done using non-surgical embryo flush techniques six days after AI. Recovered embryos were microscopically evaluated and graded on a 1 to 5 scale (1 = excellent, 2 = good, 3 = fair, 4 = poor, and 5 = degenerate) to evaluate embryo quality.

Results across both locations were combined to illustrate the effects of nutrient restriction on early embryonic development. Nutrient restriction immediately following AI resulted in poorer quality embryos that were developmentally retarded as indicated by being at an earlier stage of development and having fewer total blastomeres In addition, embryos from nutrient restricted heifers had a decreased (P = 0.01) percentage of live blastomeres.

These results suggest that the early embryo, oviduct, and uterus are sensitive to immediate changes in nutrition. Nutritional inputs to reproducing beef cows must be managed to allow for the animal to be in a positive energy balance. However the researchers indicated caution is warranted as over-nutrition may also compromise various reproductive parameters.