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Nutritional management strategies to improve growth and feed efficiency of prepubertal dairy heifers
The future of the dairy industry depends on well-developed replacement heifers. Emphasis on improving pre-weaned calf nutrition has predominated in the industry, but opportunities exist to improve nutrition and management of heifers post-weaning. We aimed to investigate common feed management strategies seen in the industry and their effects on growth, feed efficiency (FE), and rumen development of heifers 4 to 8 mo of age. Studies were designed as pen- and individually-fed animal trials, with data analyzed as repeated measures using PROC MIXED of SAS. Delivering feed using a total mixed ration (TMR) is common practice on dairy operations, as nutrients are delivered consistently with increased labor efficiency. We compared feeding a common diet delivered by feeding hay and concentrate separately (HF), hay side-dressed with concentrate (SBS), and a TMR, observing that FE of HF- and SBS-fed heifers was 8 to 10% greater overall compared to heifers fed a TMR (P=0.10). Additionally, HF-fed heifers were 13.5 kg heavier (P<0.01) at the end of the study and had 5.6% greater DMI overall (P<0.01) compared to SBS- and TMR-fed heifers. Since FE was improved when concentrate was fed separate from forage, we subsequently researched increasing proportions of dietary concentrate for growing heifers and the effects when switched to a high forage diet. Heifers fed 80% concentrate were the heaviest, tallest, and most feed efficient during the treatment period (P<0.01), but performed poorly when switched to a high forage TMR (60% hay) compared to heifers previously fed 60% or 40% concentrate. Additionally, molar proportions of propionate (P<0.01) and butyrate (P=0.03) were greater when heifers were fed 80% or 60% concentrate, potentially influencing rumen development. We then evaluated diets differing in non-fiber carbohydrates (NFC) in order to alter rumen fermentation and increase FE. Interestingly, heifers fed low NFC diets with added fat had higher ADG (P=0.05) and FE (P=0.07) compared to heifers fed high NFC diets despite similar dietary ME and CP content. However, in a concurrent study evaluating low and high NFC diets with individually-fed animals, ADG (P=0.02) and frame height (P=0.03) were increased for high NFC-fed animals. Overall, our results suggest feeding diets with highly digestible carbohydrates to promote greater FE and skeletal growth post-weaning. Greater understanding of the effects of feed management strategies on growing heifer performance has been achieved from our research, allowing more precise feeding recommendations and development of feeding programs to improve heifer management.
Keywords: heifer, growth, feed efficiency