The Effects of Accelerated Growth Rates and Estrogen Implants in Prepubertal Holstein Heifers on Growth, Feed Efficiency, and Blood Parameters

Abstract

Sixty-eight Holstein heifers were used to determine the effects of accelerated growth rates by increased nutrient intake and estrogen implants on feed efficiency, structural growth, and blood parameters in heifers between 19 and 39 wk of age. At the beginning of the treatment period, the heifers were assigned to one of four treatment groups by using a randomized complete block design in a 2 x 2 factorial arrangement. The treatments were standard growth rate (700 g/d), accelerated growth rate (1000 g/d), standard growth rate with an estradiol implant, and accelerated growth rate with an estradiol implant. All heifers received the same diet, but dry matter intake was adjusted weekly to achieve the target rate of gain. Accelerating heifer growth rates from 705 to 1007 g/d improved feed efficiency 5.1%, increased the rate of withers height, heart girth, and hip width growth 12, 27, and 27%, respectively, and body condition scores 0.25 points. Estradiol implants improved feed efficiency 2.4% and decreased the rate of withers height 6% and heart girth growth 3.5%. Increased nutrient intake and average daily gain depressed mean plasma growth hormone and urea nitrogen content 17 and 7%, respectively, while elevating insulin-like growth factor-1 levels by 10%. Estradiol implants increased mean plasma growth hormone content by 29% and insulin-like growth factor-1 levels by 17%, but decreased urea nitrogen content by 11%. Feeding prepubertal heifers for accelerated growth rates increased structural growth with a small increase in body condition, whereas estradiol implants improved feed efficiency and decreased the growth rate of withers height and heart girth without affecting the rate of hip width growth.

IGF‐I mRNA levels in bovine satellite cell cultures: Effects of fusion and anabolic steroid treatment

“…Additionally, it is not clear whether muscle IGF‐I mRNA levels are increased by direct action of E 2 and/or TBA or whether IGF‐I mRNA levels are elevated as an indirect response to steroid‐induced changes in the level of some other growth factor such as somatotropin. The potential role of somatotropin is of particular interest since there are conflicting reports as to whether circulating somatotropin levels are increased by steroid implantation (Hunt et al, 1991; Hayden et al, 1992, 1993; Lammers et al, 1999; Hassanab et al, 2001). Our current data demonstrate that IGF‐I mRNA levels are increased by treating proliferating BSC cultures with either E 2 or trenbolone; thus, establishing that these steroids directly stimulate production of IGF‐I in these cultures.…”

Self-assembly molecularly imprinted polymers of 17β-estradiol on the surface of magnetic nanoparticles for selective separation and detection of estrogenic hormones in feeds

“…The existence of estrogens in aquatic environments has recently been reported [3][4][5]. In addition, some estrogens that are used in the animal feeds promote growth rate and enhance fat deposition of animals [6]. Estrogenic hormones, such as 17␤-estradiol (E2), estrone (E1) and estriol (E3), exhibit high degrees of estrogenic activity.…”

Dietary urea, exogenous estradiol-17β, and nitrogen utilization in Holstein steers fed a low-protein diet

“…The numerical elevation of PUN observed when E 2 was administered to steers consuming the control diet is very small and is considered within normal variation. Lammers et al (1999) observed an 11% decrease in PUN concentration in prepubertal heifers fed for growth rates of either 700 or 1000 g d -1 and implanted with E 2 .…”