Graduate Thesis Or Dissertation
 

Puberty development and reproductive performance in beef heifers fed rations supplemented with Oregon by-product feeds

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/js956j11m

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  • In the majority of management scenarios, it is imperative that beef replacement heifers calve at two years of age. In order to achieve this goal, yearling heifers should reach 60 to 65% of their mature body weight by 13 months of age. Feed costs represent 75 to 80% of the total costs incurred by a beef producer in the development of replacement heifers. At current beef prices, it takes at least three live calves before the heifer development period is paid. Feed costs have become more problematic and volatile in recent years. Increasing pressure for the use of grains in brewing and for ethanol production has inflated feed prices. Demand for grain has also resulted in more ground being taken out of forage production which has resulted in much higher hay prices. However, the increased use of feedstuffs by fermentation industries results in by-product feeds that can be utilized best by beef cattle. Utilization of these by-product feedstuffs by cattle not only results in cheaper feed, and therefore production costs, but also enhances the sustainability of the fermentation industry. The objective of this research was to evaluate puberty onset and subsequent reproductive performance in heifers fed a traditional ration with grass hay to rations in which grass hay was substituted with either grass-seed straw or a grass seed straw-brewer's grain silage. Eighteen heifers (initial body weight = 561±11.4 lbs and age = 278±2.4 d) were randomly assigned to one of three treatment groups: grass hay (HAY), grass seed straw (STRAW), or grass seed straw-brewer’s grain silage (SILAGE). Heifers were individually fed twice daily using Calan gates for 22 weeks. Heifers were weighed and 10-ml blood samples were recovered weekly. Plasma was recovered by centrifugation and stored at -20° C until analyzed for progesterone and Anti-Mullerian Hormone (AMH) concentrations. Puberty onset was defined as plasma progesterone exceeding 1 ng/ml. At week 21, heifers were estrous-synchronized using a CIDR-Select Synch protocol. Heifers displaying estrus were inseminated 12 h after onset with one straw of frozen semen. Heifers not displaying estrus were injected with PGF₂α 10 d after the initial PGF₂α injection in the CIDR-Select Synch protocol and subsequently observed for estrus and inseminated as described. Mean ages and weights of heifers were similar (P>0.10) across all treatments at the start of the feeding period. Heifer ages at puberty did not differ (P>0.10) due to treatment. Average daily gain of heifers during the feeding trial fed SILAGE were lower (P<0.0005) than heifers fed either HAY or STRAW, However, no differences (p>0.10) were found in body weight at puberty onset. However, body weights of heifers fed SILAGE were lower (P<0.05) than heifers fed either HAY or STRAW at the starts of the breeding and calving seasons. No differences (P>0.10) in services per conception, calving ease scores, calf vigor scores, or calf birth weights were observed between treatments. These results suggest that heifers fed the less expensive, by-product STRAW ration have weight gain and reproductive performance similar to heifers fed a traditional HAY ration. Although heifers fed the SILAGE diet had lighter body weights, a negative impact on reproductive measurements was not observed, suggesting the ration was adequate to support reproductive performance similar to a traditional HAY ration.
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