Responses in growing pigs to lysine and threonine limiting feeds and environmental temperature.

Thesis (M.Sc. Agric.)-University of Natal, Pietermaritzburg, 1996.

In this thesis two experiments were conducted. The objective of the first experiment was to measure the response of a range of dietary threonine concentrations and environmental temperatures on the performance of young pigs. Large White x Landrace entire male pigs (n=48) at 12 kg live weight were assigned to one of six dietary threonine treatments (n=2) and one of four temperature treatments. Dietary threonine concentrations were formulated as 8.9 g Threonine/kg food (T1); 6.7 g/kg (T2); 6.2 g/kg (T3); 4.9 g/kg (T4); 3.6 g/kg (T5); 4.9 g/kg (T6). To check that threonine was limiting the most diluted diet (T5) was supplemented with synthetic threonine. The animals were fed ad libitum and housed in environmentally-controlled facilities. The experiment was conducted using four different temperature regimes; 18.1 (±0.38)°C, 21.9 (±0.19)°C, 26.1 (±0.50)°C and 29.9 (±0.34)°C. On reaching 25 kg live weight the pigs were slaughtered and the carcasses prepared to obtain samples for carcass analysis. There were significant differences (P < 0.001) in the rate of growth (ADG) between dietary treatments with the highest gains on T1 (0.571 kg/d). There were significant differences (P < 0.01) in ADG between temperature treatments with the highest growth rate at 22°C (0.527 kg/d) and the lowest at 30°C (0.428 kg/d). Food intakes were significantly affected by temperature (P < 0.001) and unaffected by dietary threonine concentrations. There was a 26.1 % increase in feed intake at 18°C when compared to the feed intake at 26°C. The highest FCE was recorded at 26°C (449 g gain/kg food) and the lowest at 18°C (386 g gain/kg food). There was an 18.4% reduction in body protein content at 25 kg live weight between pigs fed on Tl as opposed to those fed on T5. Dietary treatment had a significant effect (P < 0.001) on the fat composition of the empty carcass. The highest fat content was on T5 (4.898 kg) and the lowest on T1 (2.041 kg). Temperature had a significant effect (P < 0.001) on lipid growth rates. Threonine accretion rates were higher (P < 0.001) for pigs fed on T1 (3.52 g/d) than those fed on T2 to T5. The lowest threonine retention was on T5 at 1.49 g/d. Linear regression of daily carcass threonine accretion on daily threonine intake resulted in an efficiency of threonine utilization for pigs between 12 kg and 25 kg live weight of 38%. The objective of the second experiment was to measure the response of dietary lysine concentrations and environmental temperature on the performance of young pigs. Large White x Landrace entire male pigs (n=48) were assigned to one of six dietary lysine treatments (n=2) and one of four temperature treatments. Dietary lysine concentrations were formulated as 12.7 g Lysine/kg food (T1); 10.8 g/kg (T2); 8.9 g/kg (T3); 7.0 g/kg (T4); 5.1 g/kg (T5); 7.0 g/kg (T6). To check that lysine was limiting, the most diluted diet (T5) was supplemented with synthetic lysine. The animals were fed ad libitum and housed in environmentally controlled facilities. The experiment was conducted using four different temperature regimes; 18.1 (±0.19)°C, 22.0(±O.17)°C, 25.7 (±O.32)°C and 29.6 (±O.40)°C. On reaching 25 kg live weight the pigs were slaughtered and the carcasses prepared for chemical analysis. There were significant differences (P < 0.001) in ADG between dietary lysine treatments, with the highest gains on T1 (0.621 kg/d) and the lowest on T5 (0.395 kg/d). There were significant differences (P < 0.001) in ADG between temperature treatments, with the highest growth rate at 22°C (0.588 kg/d) and the lowest at 30°C (0.466 kg/d). Food intakes were significantly affected by dietary treatment (P < 0.05) and environmental temperature (P < 0.001). The highest feed intake was on T4 (1.284 kg/d) and the lowest on T1 (1.080 kg/d). There was a 21.4% increase in feed intake at 18°C (1.394 kg/d) when compared to the feed intake at 30°C (1.096 kg/d). The highest FCE was recorded at 22°C (491 g gain/kg food) and the lowest at 18°C (417 g gain/kg food). There was an 19.9% reduction in body protein of pigs at 25 kg live weight fed on T1 (3 .715 kg) as opposed to those fed on T5 (2.976 kg). Dietary treatment had a significant effect (p < 0.001) on the fat content of the empty carcass. There was an increase of 134% in the fat content of the empty carcass between those pigs fed on T5 as opposed to those fed on T5. The highest fat content was on T5 (4.926 kg) and the lowest on T1 (2.103 kg). There were significant differences in protein accretion rates (p < 0.001) between the dietary and temperature treatments. The highest PR was on T1 (91.85 g/day) and at 18°C (77.08 g/day). The highest THL (P < 0.05) was at 18°C (12.84 MJ/d). Lysine accretion rates were highest on T1 (6.475 g/d) and lowest on T5 (2.726 g/d). Linear regression of daily carcass lysine accretion on daily lysine intake showed that the efficiency of lysine utilization for pigs between 12 kg and 25 kg live weight was 37%.