Document Type

Dissertation - Open Access

Award Date

2019

Degree Name

Doctor of Philosophy (PhD)

Department

Animal Science

First Advisor

Joseph P. Cassady

Second Advisor

Kristin E. Hales

Keywords

backgrounding, cattle hay, rate of gain, receiving, silage

Abstract

Management of cattle during the receiving and backgrounding phases can influence the performance of feedlot cattle. The receiving phase is a stressful time for cattle entering the feedlot and quickly adapting cattle to milled feed can impact their productivity. Silages are often viewed as less desirable feedstuffs in receiving diets for newly-weaned calves. The objective of this 2-yr study was to evaluate effects of roughage source in receiving diets on cattle performance, diet mixing, and diet integrity. Steer calves (yr 1, n = 180; yr 2, n = 210) were weaned and immediately transported 580 km. Calves were allotted to 1 of 3 receiving diets differing only in oat forage as the roughage source: oat hay (HAY), oat hay with added water (HAYW), or oat silage (SIL). Diets were fed for 42 d. Bunk samples were collected at feed delivery and postmeal and subjected to particle separation using a 12.7 mm screen. An initial overestimate of SIL dry matter (DM) in yr 1 caused steers on the SIL diet to be offered less (P < 0.01) DM than HAY or HAYW steers from d 1 to 16. Regardless, average daily gain (ADG) was not different (P ≥ 0.16) during this time. Cumulatively, no differences in ADG (P = 0.24) or gain:feed (G:F; P = 0.47) were observed, but HAY steers consumed less (P = 0.02) DM than HAYW or SIL steers. In yr 2, SIL steers had greater (P = 0.01) ADG during the initial 14 d compared to HAY or HAYW steers with no difference in dry matter intake (DMI; P = 0.18); thus SIL steers had greater G:F (P = 0.01). Cumulatively, no differences in ADG were observed in yr 2 (P = 0.21); however, SIL steers consumed less (P < 0.01) DM than HAY or HAYW steers which resulted in greater G:F (P = 0.01). Circulating lipid concentrations tended to be greater for HAY cattle compared to HAYW or SIL cattle (P = 0.09). The magnitude of change in the proportion of larger particles in the bunk from delivery to post-meal (i.e. the effect or sorting) was nearly 4-fold greater for HAY than SIL in yr 1 (P = 0.04) and 3.5-fold greater in yr 2 (P = 0.05). As batch fraction (BF) increased, when batch was offloaded from the mixer, the proportion of larger particles delivered also increased (P < 0.01). Conversely, cumulative ADG decreased (P < 0.01) as BF increased. In conclusion, SIL had no adverse effects on the growth performance of newly-weaned calves. Diet mixing and integrity can be improved by adding SIL in receiving diets, as indicated by more uniformity of particle size throughout the batch and less change in particle size uniformity from delivery to postmeal. Effects of varying backgrounding phase growth rate (BGR) on subsequent finishing phase performance and carcass characteristics were evaluated in 2 experiments. In Exp. 1, 240 steers were randomly assigned to 1 of 3 BGR treatments from study initiation to 397 kg: 0.91 kg/d (LOW), 1.13 kg/d (MID), or 1.36 kg/d (HIGH). Net energy equations were used to prescribe sufficient DM to achieve each the BGR for each group. When each treatment reached the target body weight (BW) of the backgrounding phase, it was transitioned to a finishing diet. From this point on, treatments were managed similarly. The cattle within each treatment were harvested independently at a common 12th-rib fat endpoint. By design, backgrounding phase ADG linearly increased (P < 0.01). The backgrounding phase lasted 92, 78, and 62 d for LOW, MID, and HIGH, respectively. Finishing phase ADG and DMI were linearly decreased with greater BGR (P < 0.01), but no difference in G:F was observed (P ≥ 0.35). Cumulatively, ADG linearly increased with greater BGR (P < 0.01), but G:F was not different (P ≥ 0.17). Hot carcass weight (HCW) decreased linearly with greater BGR (P < 0.01). Marbling score responded quadratically as it increased from LOW to MID, then decreased with HIGH BGR (P = 0.02). In Exp. 2, 144 steers were randomly assigned to the same 3 treatments used in Exp. 1. Backgrounding phase endpoint BW was 408 kg in Exp. 2. As expected, backgrounding phase ADG linearly increased (P < 0.01). The backgrounding phase lasted 76, 61, and 54 d for LOW, MID, and HIGH, respectively. Finishing phase ADG and DMI linearly decreased (P ≤ 0.02) as BGR increased, with no difference in G:F (P ≥ 0.16). Cumulative ADG linearly increased with greater BGR (P = 0.02) while G:F also tended to increase (P = 0.07). Restricting BGR linearly increased HCW (P = 0.04). Similar to Exp. 1, marbling score tended to respond quadratically to increasing BGR as it increased from LOW to MID, then decreased between MID and HIGH (P = 0.06). When regressing marbling scores from Exp. 1 and 2 on BGR, we found that marbling responded quadratically (P = 0.03) and BGR accounted for approximately 8% of the variation in marbling score. Restricting BGR can result in improved finishing phase performance and greater final BW; however, a greater number of days on feed is required. Increases in HCW can also be achieved with lesser BGR, although optimum carcass quality may be realized with only modest restriction in BGR.

Format

application/pdf

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

Included in

Beef Science Commons

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