Effects of growth rate on carcass composition and lipid partitioning at puberty and growth hormone, insulin-like growth factor I, insulin, and metabolites before puberty in beef heifers2

Abstract

The effect of three rates of gain on carcass composition, lipid partitioning, age and BW at puberty, and concentrations of growth hormone (GH), IGF-I, insulin, glucose, and NEFA in plasma were evaluated in 38 Angus x Hereford heifers. Heifers were allotted by BW and age to three treatments with a replication in each of 2 yr: full-fed (n = 13; FF) to gain 1.36 kg/d; limit-fed (n = 12; LF) to gain .68 kg/d; maintenance-full-fed (n = 13; MFF) to gain .23 kg/d for 16 wk, then full-fed to gain 1.36 kg/d. Heifers were slaughtered within 10 d after the onset of puberty. At slaughter, kidney, pelvic, and heart fat (KPH) and udder (UDDER) were separated from carcass, as was fat surrounding viscera (OM). After 48 h at 4 degrees C a carcass side was dissected into subcutaneous fat (SC), intermuscular fat (SEAM), soft tissue (SFT = inseparable lean and fat), LEAN, and BONE. In yr 1, LF heifers (431 d) were older (P < .05) than MFF heifers (371 d) at puberty, but age of FF heifers (389 d) did not differ (P > .10) from that of LF and MFF heifers. In yr 2, FF heifers (351 d) were younger (P < .05) than LF and MFF heifers (398 and 434 d, respectively). The FF heifers had greater (P < .05) BW and a greater (P < .01) percentage of lipid in the carcass at puberty than LF and MFF heifers. During the first 16 wk of treatment, concentrations of NEFA were greater in heifers with slower daily gains (MFF > LF > FF; P < .01). Concentrations of NEFA were lesser and concentrations of IGF-I and insulin were greater in plasma of FF than in that of MFF heifers during the 10 wk before puberty. Treatment significantly altered age, BW, carcass composition, and lipid partitioning at puberty in beef heifers. We conclude that the percentage of body fat is not the sole regulator of puberty, and age may be an important modulator in determining the onset of puberty in beef heifers.

The value of reproductive tract scoring as a predictor of fertility and production outcomes in beef heifers1

“…This is in contrast with an older theory that a heifer needs to reach a specific level of somatic development (BW) for the onset of puberty to be induced (Day et al, 1984(Day et al, , 1987Foster, 1994) and may indicate that there is Reproductive tract scoring in beef heifers an age-related induction of puberty that is not related to the BW of the heifer, in agreement with Yelich et al (1995) and Pence et al (2007). On the other hand, it may also indicate some variation in the critical BW of individual heifers that needed to be achieved to induce puberty, meaning that there was some scope for selection for AP in this population.…”

Effect of high energy intake on carcass composition and hypothalamic gene expression in Bos indicus heifers

“…Some authors observed that females became pubertal with a greater weight and BCS when subjected to a high-energy diet (Pattherson et al, 1990;Hopper et al, 1993;Yelich et al, 1995). In the present study, LMA was increased by high energy intake as was the cold carcass weight.…”

Creep-feeding to stimulate metabolic imprinting in nursing beef heifers: impacts on heifer growth, reproductive and physiological variables

“…The lack of treatment effects on plasma insulin on day 51 was unexpected because circulating insulin is also positively regulated by nutrient intake and glucose concentrations (Vizcarra et al, 1998). On the other hand, the greater plasma insulin concentration in CON heifers on days 261 and 325 support treatment trends (P = 0.09) detected on ADG during the development phase (Table 3), corroborating that CON heifers had more dietary nutrients available for growth during this period (Yelich et al, 1995;Hess et al, 2005). No treatment effects were detected (P = 0.35) on plasma leptin concentrations (Table 5), although circulating leptin concentration is regulated by nutrient intake and insulin (Houseknecht et al, 1998).…”