The effect of increasing standardized ileal digestible histidine:lysine ratio during lactation on sow and litter performance

The NRC (2012) requirement estimate for His is approximately 20 g/d for lactating sows. This estimate is based on factorial models and there is limited empirical data available. A total of 88 lactating sows (Line 241, DNA) and their litters were used to evaluate the effects of increasing standardized ileal digestible (SID) His:Lys ratio on sow and litter performance. Sows were blocked by parity and body weight (BW) on approximately d 110 of gestation and allotted to one of three dietary treatments containing increasing SID His:Lys ratios (40, 50, or 60% of Lys). The 40% His:Lys ratio diet was corn and soybean meal-based and formulated to 1.05% SID Lys with no added L-His. Sows were allowed 2.72 kg/d of their treatment diet from d 110 of gestation until farrowing after which they were provided ad libitum access to treatment diets. Pigs were cross-fostered by d 2 of lactation within treatment to equalize litter size (approximately 14.2 pigs). Sow BW, backfat, caliper score, and loin depth on d 110 of gestation and at weaning was not affected (P > 0.10) by increasing SID His:Lys ratio. Increasing SID His:Lys ratio tended (linear, P = 0.085) to decrease percentage of pigs born alive due to an increase (linear, P = 0.049) in the percentage of stillborn pigs. Litter weight on d 7 and the day before weaning (d 17) tended to increase and then decrease (quadratic, P ≤0.062) as SID His:Lys ratio increased. Pig average daily gain (ADG) from d 7 to d 17 tended to increase (linear, P = 0.10) with increasing SID His:Lys ratio, though litter ADG and pre-weaning survival remained unaffected (P > 0.10). Increasing SID His:Lys ratio increased and then decreased (quadratic, P = 0.027) calculated total milk yield from d 2 of lactation until d 17 and tended to increase and then decrease calculated average daily milk yield (quadratic, P = 0.078), but did not affect milk composition (P > 0.10). Daily feed intake averaged 7.1 kg/d across the three treatments and SID Lys intake averaged 74.6 g/d. Average SID His intake was 29.0, 38.0, and 44.9 g/d with increasing SID His:Lys ratio, exceeding NRC (2012) requirement estimates. These results suggest that a SID His:Lys ratio of 50% tended to increase calculated average daily milk yield and litter weight on d 7 and the day before weaning. Additional empirical requirement studies are warranted to reevaluate current NRC (2012) requirement estimates.