Effect of anabolic hormone exposure during the backgrounding-phase in calf-fed steers of different mature sizes1

Abstract

The mature size (MS) of cows in the United States is diverse, which leads to diversity in the MS of feeder cattle and hot carcass weights (HCW) of fed cattle. Cattle feeders must manage this inherent variation. Given that implants alter MS, they may be an effective tool to manage variation in HCW across groups of cattle. Two experiments were conducted to evaluate the interaction of MS and implant status in calf-fed steers. Steer calves from the same two sources were used in both experiments. Because breeding seasons were <60 d, it was assumed that weaning weight (WW) to a large extent reflected differences in MS. Smaller MS (SMS) and larger MS (LMS) steers were identified from the tails of the WW distribution. Within each MS group, steers were implanted with 20 mg estradiol benzoate and 200 mg progesterone (SS) or 14 mg estradiol benzoate and 100 mg trenbolone acetate (CH) on d 1 (Exp. 1), and nonimplanted (NI) or implanted with SS on d 2 (Exp. 2). In both experiments, a common terminal implant was used and steers were fed for 161 (Exp. 1) and 168 d (Exp. 2). Data were analyzed as a randomized complete block design with a 2 × 2 factorial treatment structure, with main effects of MS and implant. No MS × implant interactions were observed in either experiment (P ≥ 0.08). In both experiments LMS steers had heavier body weights (BW), HCW, and BW adjusted to 28% empty body fat (AFBW), greater average daily gain (ADG), dry matter intake (DMI), and lesser gain:feed (G:F) than SMS steers (P ≤ 0.02). No differences were evident in marbling score or Quality Grade distributions between SMS and LMS steers (P ≥ 0.13). In Exp. 1, no differences in growth performance, carcass traits, AFBW, or calculated frame size (FS) were observed for steers initially implanted with SS or CH (P ≥ 0.12). In Exp. 2, steers implanted initially with SS had heavier final BW, greater ADG and DMI (P ≤ 0.01), and similar G:F (P = 0.78) than NI steers. Steers initially implanted with SS had heavier HCW (P < 0.01), but no other differences in carcass characteristics were observed (P ≥ 0.23). Additionally, steers implanted with SS tended to have heavier AFBW (P = 0.07) and greater calculated FS (P = 0.05) than NI steers. Steers of different MS responded similarly to implants. Previous exposure to implants did not alter the response to the terminal implant. Estradiol increases the FS of steers; however, when similar doses of estradiol are compared, trenbolone acetate did not further increase FS (Exp. 1).

Nose Color of Charolais × British Crossbred Beef Steers Alters Body Weight at a Common Degree of Fatness and Marbling Score in Steers Reared Under Similar Management from Birth through Finishing

“…Greater weaning weight did not result in greater final shrunk BW and resulted in decreased mature BW (BW at 28% EBF) in the present study. This finding is in contrast to what has been demonstrated previously (Gentry et al, 2020). Hot carcass weight was similar between nose classification, but RF and USDA marbling scores differed.…”

“…Hot carcass weight was similar between nose classification, but RF and USDA marbling scores differed. Steers from the black nose classification were fatter at harvest as indicated by greater RF depth and greater estimated EBF and this is to be expected when the values used to calculated this variable differed and the fact that RF carries the highest input in the regression equation used to determine EBF (Guiroy et al, 2001;2002;Smith et al, 2018;Gentry et al, 2020). To answer the question of whether increased marbling scores observed for the black nosed steers was an artifact of progression in the growth curve or due to increased RF, this finding was further investigated using the mRatio.…”

“…Few studies have illustrated the economic value of differing breeds and phenotypes of feeder cattle (Halfman et al, 2009;McCabe et al, 2019) and to our knowledge no studies have investigated differing genotypes and phenotypes of steers calves maintained under similar management from birth, through weaning, backgrounding and finishing and subsequently through the harvest process. Gentry et al (2020) indicated that some producers might use visual appraisal to recognize differences in frame size and subsequently observe difference in marbling and conclude that marbling is inversely related to frame size. Weaning weight was greater in black nosed steers compared to pink nosed steers.…”

“…Weaning weight was greater in black nosed steers compared to pink nosed steers. Gentry et al (2020) indicated that weaning weight could be used as a proxy for frame size determination if calves were managed under similar conditions and of similar age at the time of weaning. Steers used in the present analysis were from a calving season that was approximately 60-d in length, thus it is assumed that the steers calves used in the present analysis were of similar age.…”

“…There is inherent variation in the feeder cattle population in the United States. These differences are related to cattle mature size, growth performance, health outcomes and carcass quality and yield grade (Gentry et al, 2020;Smith et al, 2020). These differences can create issues in relation to management of fed cattle populations and harvesting at the appropriate time in order to not receive discounts for cattle that do not meet specific grid specifications for weight, quality and cutability.…”