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Multiparous Large White sows (n = 63) were used to investigate the effects of five ambient temperatures (18, 22, 25, 27, and 29 degrees C) and two dietary protein contents on their lactation performance. At each temperature treatment, ambient temperature was maintained constant over the 21-d lactation period. Dietary protein content was either 14 or 17% with essential amino acids levels calculated not to be limiting. The animals had ad libitum access to feed between the seventh and the 19th day of lactation. Diet composition did not influence lactation performance. Over the 21-d lactation, feed intake decreased from 5.67 to 3.08 kg/d between 18 and 29 degrees C. Between d 7 and 19, the corresponding values were 7.16 and 3.48 kg/d, respectively. This decrease was curvilinear; an equation to predict voluntary feed intake (VFI) from temperature (T, degrees C) and body weight (BW, kg) is proposed: VFI = -49,052 + 1,213 T - 31.5 T2 + 330 BW - .61 BW2 (residual standard deviation: 1,018). Skin temperature increased regularly with increased ambient temperature (34.6 to 37.4 degrees C between 18 and 29 degrees C), whereas udder temperature reached a plateau at 25 degrees C (38.3 degrees C). The gradient of temperature between skin and rectum was minimal (2 degrees C ) at 27 degrees C and remained constant at 29 degrees C. This constancy coincides with the marked reduction of feed intake. The respiratory rate increased from 26 to 124 breaths/min between 18 and 29 degrees C, and this indicates that the evaporative critical temperature was below 22 degrees C. The BW loss increased from 23 to 35 kg between 18 and 29 degrees C, but its estimated chemical composition remained constant. Pig growth rate was almost constant between 18 and 25 degrees C (241 g/d) and was reduced above 25 degrees C (212 and 189 g/d at 27 and 29 degrees C, respectively). In conclusion, temperatures above 25 degrees C seem to be critical for lactating sows in order to maintain their performance.

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Within-litter variation of piglet birth weight (BW0) is associated with an increased piglet mortality and a high variability in pig weight at weaning and weight or age at slaughter. Data collected in two experimental herds were used to quantify within-litter variability in BW0 and to assess the influence of factors mainly related to the sow. Within 24 h after birth, piglets born alive were individually weighed and stillborn piglets were collectively (first data set) or individually (second data set) weighed. The first data set was restricted to litters with no or only one stillborn piglet (3338 litters). It was used to assess the influence of genetic selection on BW0 variation by comparing litter characteristics before (1994 to 1996) and after (2001 to 2004) the development of hyperprolific sows in this herd. The second data set included all litters (n 5 1596) from sows born between 2000 and 2004. For each litter, mean BW0 (mBW0) and its coefficient of variation (CV BW0 ) were calculated. Then, variance analyses were performed to test the influence of litter size, parity, year of sow birth and season at conception. Prolificacy improvement was associated with an increased CV BW0 in litters from pure Large White (LW) and Landrace 3 Large White (LR 3 LW) crossbred sows. The CV BW0 averaged 21% and was significantly influenced by litter size and parity. It increased from 15% to 24% when litter size varied from less than 10 piglets to more than 15 piglets. The proportion of small piglets (i.e. weighing less than 1 kg) increased concomitantly. The CV BW0 was not repeatable from a parity to the following. It was lowest for first and second parities (20%) and thereafter increased progressively. The CV BW0 was positively related to sow's backfat thickness gain during gestation. Taking into account litter size, parity, year of sow birth and season at conception explained 20% of BW0 variation. Thus, major part of heterogeneity is due to other factors, presumably including embryo genotype, on the one hand, and factors that influence embryo and foetus development, such as epigenetic factors, on the other hand.

The effect of dietary NE content on feed intake and performance of pigs was investigated using crossbred barrows with initial and final BW of approximately 35 and 110 kg, respectively. Pigs were housed individually and allowed ad libitum access to feed. Pigs were randomly allotted to 6 wheat and soybean meal-based diets (8.1, 8.7, 9.3, 9.9, 10.5, and 11.1 MJ NE/kg) with 16 pigs/diet. Ratios between standardized ileal digestible AA and NE were similar in all diets. Over the entire experiment, increase in dietary NE concentration was associated with a decreased ADFI (3.216, 3.216, 3.122, 2.910, 2.732, and 2.684 kg/d, respectively, for diets containing 8.1 to 11.1 MJ NE/kg; linear, P < 0.01). The NE intake increased as dietary NE increased from 8.1 to 11.1 MJ NE/kg (26.04, 27.98, 29.03, 28.81, 28.68, and 29.77 MJ/d, respectively; linear, P < 0.01, and quadratic, P = 0.06). Average daily gain increased when dietary NE concentration increased (1.046, 1.126, 1.135, 1.177, 1.156, and 1.152 kg/d, respectively, for diets containing 8.1 to 11.1 MJ NE/kg; linear and quadratic, P < 0.01). The increase in dietary NE concentration was associated with an increase in dressing percentage (76.5, 77.0, 77.4, 78.0, 78.2, and 78.4% of BW; linear, P < 0.01) but no differences in lean percentage (58.3, 57.9, 58.0, 57.3, 58.1, and 56.4% of HCW, respectively, for diets containing 8.1 to 11.1 MJ NE/kg; P = 0.12). When dietary NE concentration increased from 8.1 to 11.1 MJ/kg, the G:F increased (0.326, 0.352, 0.364, 0.405, 0.425, and 0.428 kg/kg, respectively; linear, P < 0.01), but the G:F expressed using the NE system did not change (G:F, 39.97 g/MJ NE; P = 0.44). When adjusted to the same dressing yield and lean percentage, the differences in adjusted ADG increased among treatments, but the adjusted G:F expressed using the NE system was not influenced by dietary energy concentration. These results confirm the ability of individually housed pigs to adjust their spontaneous feed intake over a very wide range of NE concentrations (8.7 to 10.5 MJ/kg). Under commercial conditions, pigs may experience less variation in ADFI than the results obtained in this experiment because of differences in dietary energy concentrations. However, it seems that only a severe reduction in dietary energy concentration will be effective in restricting energy intake of pigs that are allowed ad libitum access to feed.