Abstract
We investigated the effects of diets differing in energy and protein concentrations given during pre- and post-weaning on hormone and metabolite levels in association to parameters of growth. Sixteen Aberdeen Angus calves four-day-old were allocated in individual pens during 105 days in a randomized complete design. Animals consumed ad libitum various diets differing in proportion of energy and protein (A: 80% of concentrate, 20% alfalfa hay; B: 60% concentrate, 40% of alfalfa hay; C: 40% concentrate, 60% alfalfa hay, and D: 20% concentrate, 80% alfalfa hay). Also, calves consumed milk substitute up to 60-day-old day. Serum growth hormone and cortisol levels were not altered with diet changes (P > 0.05) neither during the pre- nor the post-weaning periods. Plasma insulin concentration average daily intake, glucose and thyroid hormone levels, and concentrations of ammonia nitrogen and propionic acid were greater (P < 0.01) for diets having higher than lower energy and protein levels during the post-weaning but not during the pre-weaning period. These results suggest inclusion of higher amounts of concentrate in the diet of weaned calves. Key words: Calves, early weaning, energy, growth, hormones, metabolites, protein.
Highlights
Cow-calf operations are the most important activities in the temperate semi-arid rangeland region in Central Argentina known as the Caldenal (35 to 40° S, 62 to 66° W) (Fernández and Busso, 1999; Fernández, 2003; Fernández et al, 2009)
Calves fed diets having a high concentrate proportion showed greater (P < 0.01) average daily weight gains (ADWG) than those fed with higher hay fraction
Our results showed that high energy diets yield more propionic acid, which can readily be converted to glucose through gluconeogenesis in the liver (Bellver et al, 1995)
Summary
Cow-calf operations are the most important activities in the temperate semi-arid rangeland region in Central Argentina known as the Caldenal (35 to 40° S, 62 to 66° W) (Fernández and Busso, 1999; Fernández, 2003; Fernández et al, 2009). Weaning is an increasing practice management in the Caldenal and the Monte (Giorgetti et al, 2006; Kugler et al, 2008) since it tends to improve reproductive performance. This is because it generates more forage availability for reproductive functions by suppressing natural lactation. Calf nutrition during the lactating period has been considered critical for ruminant growth and maintenance of reasonable calf average daily weight gains (ADWG) after natality (Breier et al, 1986; Kugler et al, 2002)
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