Piglet birth weight as determining factor of optimal nutrient concentration in grower and finisher diets

Abstract

The selection for improved sow productivity has led to an increase in litter size as well as an increase in the number of low-birth-weight piglets born. Low-birth-weight pigs are associated with slower growth rates, lighter slaughter weights and carcasses as well as decreased pork quality compared to heavy-birth-weight pigs. Therefore, low-birth-weight pigs pose management challenges and may have negative economic implications for pork producers. Furthermore, the nutrient requirements suggested for grow-finishing pigs might therefore not be applicable to low-birth-weight pigs. The objective of this study was to determine the optimal nutrient concentration of grow-finishing diets based on birth weight and the effects on growth performance and carcass quality of low-birth-weight pigs compared to heavy-birth-weight pigs subject to the same diets. The experiment was performed on 144 pigs and consisted of three feed treatments: control (CON), high standard ileal digestible (SID) lysine (HL), and low SID lysine (LL). The energy level between treatments remained constant within each feeding phase (starter, grower, and finisher). The CON, HL and LL diets within the starter phase had an energy level of 9.87 MJ NE/kg, while the CON, HL and LL diets within the grower phase had an energy level of 9.74 MJ NE/kg and, finally, the energy level of the CON, HL and LL diets within the finisher phase were 9.67 MJ NE/kg. Thus, the diets were iso-caloric for each feeding phase; therefore, SID lysine was the only variable between the three-phase treatment diets. The ratio of the other essential amino acids relative to lysine was kept constant and according to the Feeding Manual for Topigs Norsvin Finishers (2012). A total of 48 pens were used, with three pigs per pen, providing four replicates per treatment. Each pen represented an experimental unit and was allocated to treatments following a complete randomised block design with three feed treatments (control, high SID lysine, and low SID lysine), each combined with either low-birth-weight or heavy-birth-weight pigs, as well as male and female animals. The pigs were 10 weeks (70 days) of age at the start of the trial and reared for a period of 11 weeks until slaughter. The pigs were weighed weekly and the average feed intake per pen was measured weekly as well. Average daily feed intake (ADFI), average daily gain (ADG), and feed conversion ratio (FCR) were calculated per pen. The trial continued until 21 weeks (147 days) of age after which all the pigs were slaughtered to determine carcass characteristics, including hot carcass weight, cold carcass weight, backfat thickness and lean meat percentage. During the experimental period, birth weight had significant (P < 0.05) effects on weight during the starter, grower and finisher phases of the trial, as heavy-birth-weight pigs were heavier at each phase of production compared to low-birth-weight pigs. Feed treatment had no significant (P > 0.05) effect 5 on start and end weights of the starter, grower, and finisher phases within birth weight groups. However, the heaviest slaughter weights for the heavy-birth-weight and low-birth-weight groups were observed for the low SID lysine and control treatments, respectively. The low SID lysine feed treatment had significant (P < 0.05) effects on ADG between the heavy and low-birth-weight groups for the starter, grower and finisher phases, as heavy-birth-weight pigs had higher ADG compared to low-birth-weight pigs. Throughout the experiment, heavy-birth-weight pigs had significantly (P < 0.05) higher ADG compared to low-birth-weight pigs. The highest ADG of the experiment were observed during the finisher phase and the SID lysine level required to optimise ADG from 120 to 147 days-of-age was found to be 6.84 g/kg for heavy-birth-weight pigs and 7.60 g/kg for low-birth-weight pigs. Throughout the experiment, heavy-birth-weight pigs had higher (P < 0.05) ADFI compared to low-birth-weight pigs for the low SID lysine treatment. Additionally, heavy-birth-weight pigs had on average greater feed intakes compared to low-birth-weight pigs. No significant (P > 0.05) differences for FCR were observed for feed treatment and birth weight during the experimental period. However, feed treatment had significant (P < 0.05) effects on FCR throughout the finisher phase, as the control treatment resulted in better FCR compared to the high SID lysine treatment. The SID lysine level required to optimise FCR during the finisher period (120 to 147 days of age) was found to be 6.84 g/kg. The lowest backfat thickness for the heavy-birth-weight carcasses was observed for the high SID lysine treatment (P < 0.05), however, lower carcass weights were observed for this treatment. The low-birth-weight group had the lowest backfat measurements for the low SID lysine level, but the lightest carcasses were observed for this treatment in comparison to the control SID lysine and high SID lysine treatments. This study showed that the control SID lysine level and the low SID lysine level improved growth performance for low-birth-weight pigs and heavy-birth-weight pigs, respectively. These treatments allowed for the greatest return on investment, as bigger carcasses with acceptable backfat levels were produced. Furthermore, both heavy-birth-weight and low-birth-pigs did not benefit from receiving diets with high SID lysine levels, as improvements in growth performance and carcass weight was not observed.