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

The NRC (National Research Council. 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 day 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 day 110 of gestation until farrowing after which they were provided ad libitum access to treatment diets. Pigs were cross-fostered by day 2 of lactation within treatment to equalize litter size (approximately 14.2 pigs). Sow BW, backfat, caliper score, and loin depth on day 110 of gestation and at weaning were 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 day 7 and the day before weaning (day 17) tended to increase and then decrease (quadratic, P ≤ 0.062) as SID His:Lys ratio increased. Pig average daily gain (ADG) from day 7 to day 17 tended to increase (linear, P = 0.10) with increasing SID His:Lys ratio, though litter ADG and preweaning survival remained unaffected (P > 0.10). Increasing SID His:Lys ratio increased and then decreased (quadratic, P = 0.027) calculated total milk yield from day 2 of lactation until day 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 day 7 and the day before weaning. Additional empirical requirement studies are warranted to reevaluate current NRC (2012) requirement estimates.