Nutritional management of yearling beef heifers and primiparous cows : links between growth, metabolic indicators, and reproductive outcomes
No Thumbnail Available
Authors
Meeting name
Sponsors
Date
Journal Title
Format
Thesis
Subject
Abstract
Nutrient intake is a key regulator of reproductive efficiency in beef females because of its influence on energy status, ovarian activity, and the timing of estrous cyclicity in beef heifers and the primiparous beef cow. This thesis evaluated how targeted nutrient supplementation during two critical developmental periods, the second breeding season of primiparous beef cows and prebreeding development in yearling beef heifers, affects growth, reproductive maturity, fertility outcomes, and responsiveness to estrus synchronization. The overarching objective of this thesis was to determine whether nutrient supplementation can improve reproductive outcomes and productivity in young beef females. The objective of Chapter 2 was to evaluate whether targeted nutrient supplementation during the breeding season could mitigate effects of negative energy balance and improve reproductive performance in fall-calving primiparous beef cows. Fall-calving primiparous beef cows (n = 49) received either no supplement (CON; n = 24) or a commercially formulated supplement (SUP; 4.08 kg·hd⁻¹·d⁻¹; n = 25) while consuming tall fescue hay. Supplemented cows had greater body weight (BW) at the end of supplementation (469 vs. 434 kg; P = 0.01) and lost less BW from Days 0 to 74 (−0.09 vs. −0.38 kg/d; P = 0.01). Calf weaning weight performance did not differ statistically, though unadjusted weaning weight tended to be higher for SUP calves than CON cows (210 vs. 195 kg; P = 0.08). Follicle diameter at synchronization did not differ (12.5 vs. 11.7 mm; P = 0.22), and pregnancy rates to AI were modestly higher for SUP cows than CON (50% vs. 40%, respectively ). Circulating NEFA and BHB concentrations were similar between treatments, though NEFA exhibited a treatment × date interaction (P = 0.03), indicating differences in energy metabolism across the breeding period. These results indicate that nutrient supplementation during the breeding season modestly improved BW outcomes and reduced BW loss, with modest improvements in fertility. In Chapter 3, the objective was to determine whether increasing nutrient supplementation during heifer development in a tall fescue-based forage system could enhance prebreeding growth and advance puberty onset prior to breeding. Heifers were developed to achieve either 50% or 65% of mature BW using two supplementation levels. Heifers developed to 65% of mature BW had greater BW during mid-postweaning development (285 vs. 262 kg; P = 0.01) and prior to the breeding season (329 vs. 266 kg; P = 0.01), with a higher average daily gain (ADG) throughout the entirety of the 113-d development period (0.80 vs. 0.28 kg/d; P = 0.01). A greater proportion of 65% treatment heifers had attained puberty at the start of estrus synchronization (50% vs. 3%; P < 0.01) based on ovarian development, and pelvic area was larger (147 vs. 143 mm²; P = 0.01) for the 65% treatment heifers compared to the 50% treatment heifers. Following estrus synchronization, a greater proportion of 65% treatment heifers expressed estrus prior to split-time artificial insemination (STAI) compared with 50% treatment heifers (94% vs. 66%; P = 0.005). These results indicate that achieving 65% of mature BW at breeding improved prebreeding growth and advanced reproductive maturity in yearling beef heifers grazing tall-fescue pastures. The findings from these two experiments demonstrate that targeted nutrient supplementation during physiologically demanding stages (i.e., the second breeding season in primiparous beef cows and prebreeding development in replacement beef heifers), supports growth, enhances reproductive readiness, and may improve reproductive outcomes. Such strategies can enhance herd longevity, productivity, and sustainability within beef cow–calf systems.
Table of Contents
PubMed ID
Degree
M.S.