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Whole Body and Maternal Protein Deposition in Gestating Gilts at Two Feeding Levels
Whole body protein deposition (Pd) is a main determinant of amino acid and energy requirements of gestating gilts; however data on the dynamics of Pd, including its response to energy intake, is limited. In a nitrogen (N)-balance study, fifty two gestating Yorkshire gilts (initial BW and back fat [BF] at d 29 of gestation 168.1±2.2 kg and 17.1±0.8 mm) were used to determine the effect of feeding level on whole body N retention. Gilts were placed on high or low daily feeding level (2.54 and 1.87 kg/d) of the same diet (3.30 Mcal ME/kg, 17.8% CP, 0.82% SID Lys) from 30 to 110 d of gestation. N-balance observations, based on total urine collection with urinary catheters and fecal N digestibility using an indigestible marker, were made during 4 d periods starting at d 35, 49, 63, 85, and 106 of gestation. To correct for systematic differences between N-balance observations and Pd, the NRC (2012) nutrient requirements model was forced to be consistent with observed changes in BW and BF between 39 and 110 d of gestation; the mean ratio between modelled Pd and observed N-balance was used to adjust N-balance observations. Pregnancy-associated Pd (fetus, mammary gland, uterus, and placenta) was calculated using actual litter size and average piglet birth weight with NRC (2012). Maternal Pd was calculated as the difference between total Pd and pregnancy-associated Pd. Feeding level and day of gestation affected whole body Pd and maternal Pd (P<0.01), but there was no interaction (P>0.70). Whole body Pd showed both linear and quadratic relationships with day of gestation (P<0.05). For the five respective N-balance periods across the two feeding levels, whole body Pd was 87.1, 74.2, 90.5, 97.1, and 107.9 (SEM=7.1) g/d. Across the five N-balance periods, total (as well as maternal) Pd increased by 33.0±1.6 g/d as a result of the increased feed intake. Maternal Pd declined linearly (P<0.001) with day of gestation and across the two feeding levels was 78.8, 51.1, 65.7, 57.1, and 39.2 (SEM=7.1) g/d for the five respective N-balance periods. In summary, the feeding level effect on total and maternal Pd was constant throughout gestation. The gradual decline in maternal Pd with day of gestation is in contrast to NRC (2012), and has important implications for the factorial estimation of amino acid requirements of gestating gilts. Further investigation into the physiological control of the dynamic changes in maternal Pd throughout gestation is warranted.
Keywords:
gestating gilts, nitrogen retention, maternal protein deposition