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Dietary energy source effects on pregnancy rates and progesterone concentrations in heifers.

T. Davis




Dietary energy source effects on pregnancy rates and progesterone concentrations in heifers.
T. Davis*, J. Stewart, C. Gleason, N. Diaz, �. Sales, C. Timlin, Z. Seekford, A. Ealy, V. Mercadante, R. White. Virginia Tech Blacksburg, VA.

Increasing dietary glucogenic precursors may improve progesterone (P4) production and conception rates in heifers. This study measured the effects of isoenergetic, isonitrogenous diets differing in primary energy source (starch or fat) on pregnancy rates and P4 concentrations of pastured heifers. Angus cross heifers (n = 29) were balanced on BW and condition score and assigned to 1 of 2 dietary treatments: a feed supplement high in starch (27.48% starch, 2.73% fat) (n = 15) or high in fat (n = 14, 9.13% starch 9.13% fat) (n = 14). Animals were housed in 1 of 2 pastures from March to July of 2019. Treatments were delivered using the SmartFeed individualized feeding system, allowing up to 4.54 kg/d of the supplemental feed. Feed delivery began 18 d before breeding and continued through the second pregnancy diagnosis. Animals were subject to an OvSynch synchronization protocol. Blood samples were collected on d −10, 1 to 7, 10, 14, 18, 21, 24, and d 28 relative to breeding d 0 for P4 analysis. If animals showed heat after the first insemination they were rebred and were sampled for P4 on the same schedule as the first AI excluding d −10 and d 1 to 7 relative to the second AI. Pregnancy diagnosis occurred at d 28 post-AI. Pregnancy rates were analyzed using a logit model with fixed effect of treatment and a random effect of pasture. Progesterone concentrations were analyzed independently using a mixed model with fixed effect of treatment, time, their interaction, and initial P4. A random effect of pasture was also included. Conception rate at first AI was not affected by treatment (46.67% and 50.00%) but overall conception rate was higher for starch fed than for fat fed heifers (83.33% and 61.54%). Despite lower overall conception rates, heifers on the fat supplement had significantly higher P4 concentrations (P < 0.001). Additional assessment of the mechanism by which diet influences conception rates is warranted

Keywords: cattle, reproduction, nutritional supplementation.

Biography: Ty Davis originally of Fort Worth, TX had little agricultural experience growing up. However, has closed the gap between he and his peers by obtaining his BS in animal science at Oklahoma State University with a minor in agribusiness and by interning with JBS Five Rivers, JBS USA, and Gardiner Angus. He then obtained his MS at Colorado State University in Biomedical Sciences with an emphasis in Assisted Reproductive Technologies where he studied reproductive physiology. He now is a PhD student at Virginia Tech where he is studying ruminant nutrition by finding the links between nutrition and reproduction in cattle.