Effects of mixed grazing with goats and co-product supplementation on dairy heifer performance and pasture composition.

摘要

Alternative feeding strategies that reduce costs and maintain animal growth and performance improve the sustainability of livestock operations. Improving forage quality by utilizing management-intensive grazing can offer an alternative management system for rearing dairy replacement heifers. Co-products can be used to supplement pasture for young, growing animals and during times of limited forage availability and declining forage quality. A 2-yr study was conducted to determine the effects of co-grazing prepubertal Holstein heifers with Boer x Kiko goats on animal performance and pasture composition and forage DM yield of tall fescue (Festuca arundinacea) and white clover (Trifolium repens) pastures. The effects of dried distillers grains (DDGS) and soybean hull supplementation on animal growth and performance was also investigated in Year 1. In Year 1, 48 heifers (age = 134.1 d; BW = 147.4 kg) and 18 goats (BW = 39.7 kg) were randomly assigned to 12 paddocks and placed in a 2 x 2 factorial arrangement to evaluate two co-product supplements (DDGS or soybean hulls (SBH)) and two grazing strategies (heifers grazed alone (HO) or heifers co-grazed with goats (HG)). In Year 2, 36 heifers (age = 165.8 d; BW = 168.0 kg) and 12 goats (BW = 33.7 kg) were allocated to one of 6 paddocks and utilized to evaluate the same grazing strategies as in Year 1 with DDGS supplementation. In both years, two goats were randomly assigned to each paddock for HG, with the remaining goats assigned to two paddocks (3 per paddock) and grazed alone (GO).;In Year 1, overall ADG and feed efficiency were similar between supplements and grazing strategies, despite pasture and total estimated DMI being greater for HO heifers compared to HG heifers (P < 0.05). Skeletal growth was similar between supplements and grazing strategies, although all heifers lost significant amounts of BW and condition while on pasture (P < 0.01). Plasma urea N concentrations were significantly greater for heifers supplemented with DDGS after 4 wks on treatment and significantly greater for HG heifers after 8 wks on treatment (P < 0.01). In Year 2, HO heifers consumed 2.3 kg more pasture and total DM per d than HG heifers (P < 0.01), though ADG and feed efficiency were similar between grazing strategies. Final hip and withers height were greater for HO heifers compared to HG heifers (P < 0.01). Heifer PUN concentrations tended to be greater for HG heifers at 8 wks (P = 0.07), and blood glucose concentrations tended to be less for HG heifers at the end of the study (P = 0.10). During both years, overall FEC, FAMACHA scores, and PUN concentrations were similar between grazing strategies. In Year 1, presence of broadleaf weeds tended to be greater after one grazing rotation in HO pastures compared to HG pastures (15.9 and 0.7%, respectively; P = 0.09), but were similar (P = 0.12) at the end of the study with weed percentages of 16.9% in HO and 3.1% in HG. Grass DM yield tended to be greater in Year 1 in HG pastures after grazing compared to HO pastures (P < 0.10), likely attributed to changes in diet selectivity. In Year 2, prior to grazing, HG pastures tended to yield more grass, legume, and total DM than HO pastures (P < 0.10), possibly due to carry over effects from the previous grazing season. After grazing once, grass, legume, other plant species, and total DM yield were similar between grazing strategies. Grass and total DM yield tended (P < 0.10) to be greater in HO pastures compared to HG pastures after the second rotation. Legume presence was significantly greater (P = 0.04) in HG pastures at the beginning of Year 2 compared to HO pastures. Visual estimation of botanical composition at the end of Year 2 showed that HO pastures had 3.5 times more weed presence than HG pastures (P < 0.01), although clipped samples taken throughout the study had similar botanical composition between grazing strategies. Weather likely played a factor in differences between stages of forage regrowth. During this 2-yr study, co-grazing did not affect overall heifer weight gains, but did decrease feed intake, which suggests that dairy heifer replacements can be successfully managed on pasture with other livestock species without negative effects on average daily gains or feed efficiency. Additionally, supplementing pasture-fed dairy heifers with DDGS can be a viable feeding strategy for replacement heifer development.