Lambs fed two diet types in confinement had increased rates of fat deposition compared with lambs grazing pasture

T.P. Keogh, V. H. Oddy, M. B. Allworth, S. R. McGrath

Research output: Other contribution to conferenceAbstractpeer-review

Abstract

Animals fed in confinement demonstrate increased rates of fat deposition in comparison to their counterparts grazing pasture. The extent to which energy costs of activity and the composition of the diet contribute to the observed differences in body composition is unclear. In this study we used CT scanning of body composition in lambs fed differing diets in confinement and grazing lucerne pasture. Composite breed wether lambs (n = 48) were CT scanned at the start and end of a six-week feeding period to measure rates of tissue deposition. Lambs (16 per treatment) were allocated to one of three treatments: 1. Confined to individual pens and offered ad libitum feeding of either a barley grain-based pellet with a 30% inclusion of lucerne chaff (P30); 2. Confined and offered a similar pellet without the inclusion of lucerne chaff, but with lucerne hay offered separately (PH); 3. Grazing lucerne pasture (LP) as a group in a paddock (initially 2.5 ha, then 17 ha from day 17). Mean daily dry matter intake (1.72 ± 0.03 v. 1.51 ± 0.03 kg/day; P < 0.001) and metabolisable energy intake (20.8 ± 0.5 v. 18.0 ± 0.3 MJ ME/head/day; P < 0.001) was greater for P30 lambs compared with PH lambs. Estimates of feed intake were not made for LP; however, the pasture was high quality (12.0 MJ ME/kg DM, 29% CP) with sufficient availability to not restrict intake. Average daily empty body weight gain was greatest for P30 (203 ± 15 g/day; P < 0.05) and did not differ between PH (152 ± 15 g/day) and LP (150 ± 15 g/day). Rates of daily fat gain were increased for P30 (141 ± 9 g/day; P < 0.001) and PH (118 ± 9 g/day) compared with LP (83 ± 9 g/day). Daily lean tissue gain was greater for LP (60 ± 9 g/day; P < 0.05) in comparison to PH (31 ± 9 g/day), with P30 (54 ± 9 g/day) not different to other treatments. Carcass lean tissue gain did not differ between treatments (43 ± 4 g/day); however, viscera lean tissue gain was greater for LP (18 ± 3 g/day; P < 0.001) in comparison to P30 (2 ± 3 g/day) and PH (5 ± 3 g/day). The lower rates of fat gain for LP lambs are likely due to decreased energy availability for gain due to the increased rate of viscera lean tissue gain and/or the increased energy expenditure associated with walking and grazing. Low intake of lucerne hay in the PH treatment meant that it was not possible to derive an indication of activity energy costs. Research to quantify the contribution of viscera lean mass and activity energy costs to the divergent body composition of lambs fed in confinement and grazing pasture may be warranted.

Conference

Conference11th International Symposium on the Nutrition of Herbivores 2023
Country/TerritoryBrazil
CityFlorianopolis
Period04/06/2308/06/23
OtherThe International Symposium on Herbivore Nutrition (ISNH) addresses various issues related to herbivore nutrition in natural ecosystems or commercial production systems. It is the world's most important scientific forum on this topic, in which the nutrition of domestic and wild herbivores is discussed from the perspective of agroecology and sustainable intensification. The Symposium was held for the first time in South Africa (1983), later taking place in Australia (1987), Malaysia (1991), France (1995), the USA (1999), Mexico (2003), China (2007), UK (2011) and Australia (2014). In 2018, the 10th and last edition took place in Clermont-Ferrand, France, with ~500 participants from all continents. Unfortunately, due to the Covid-19 pandemic, the sequence of holding a symposium edition every four years has been disrupted. The ISNH is now resumed in its 11th edition in Brazil, for the first time in Latin America. The historical evolution of the different editions denotes the transition from the pure nutrition ecology of the first ones towards a more global contextualization of the role of herbivores in food security - particularly in developing countries - as well as issues related to the role of herbivores in greenhouse gas emissions, human food, and human well-being associated with the different production systems. The most recent editions have boldly expanded the spatial scale of herbivory analysis, which now ranges from the genome to the production system. The Brazilian edition intends to consolidate this evolution by focusing on Brazilian and Latin systems in an atmosphere of a broad exchange of scientific knowledge and cordiality.
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