Utilization of milk fatty acids by the suckling Iberian piglets.

A total of 16 pure-bred Iberian (IB) sows, all of them suckling six piglets, were used, eight of them in each of the two consecutive trials (1 and 2). Daily milk yield and composition were determined weekly over a 34-day lactation period. Within each litter, one piglet at birth and four piglets on day 35 of life were slaughtered. Milk intake per piglet tended to be greater in trial 2 (832 v. 893 g/day; P=0.066), but piglets grew at 168±3.3 g/day, irrespective of the trial. In the IB sow milk, the linoleic (LA) : linolenic (LNA) acid ratio averaged 14.6 and 15.2 in trial 1 and trial 2, respectively. A fivefold increase in piglet body fat content was observed over lactation (P<0.001). Most of this fat (81.4%) was present in the carcass. After 34 days of lactation, whole-body relative content of palmitic, palmitoleic, stearic and oleic acids were very close to those in the milk consumed, suggesting direct deposition. Daily deposition of LA derivatives and of LNA and its derivatives was found to be extremely low (<0.02 g, on average). Moreover, some of the arachidonic acid (ARA) in tissues of the IB piglet at birth disappeared throughout the lactating period. An overall fractional deposition for total fatty acids (FA) was 0.409. Fractional oxidation (disappearance) rates were 0.939 and 0.926 for n-6 and n-3 polyunsaturated FA. The overall rate of disappearance for the major non-essential FA (myristic, palmitic, palmitoleic, stearic and oleic acids), estimated as 1-the overall fractional deposition rate, was 0.546. It is concluded that the high degree of FA unsaturation, high oxidation rate of LA and LNA, and poor synthesis of ARA from LA and of docosahexaenoic acid from LNA found in the suckling piglet might increase the energy cost of whole-body fat accretion, a contributor to the observed low efficiency of use of milk energy for growth.

Utilization of milk amino acids by the suckling Iberian piglet.

Sixteen pure-bred Iberian (IB) sows were used in two trials to determine the efficiency of utilization of milk protein and amino acid (AA) for growth in suckling piglets. It was hypothesized that there may be one or more strongly limiting essential AA (EAA) responsible for the slow rate of growth of the IB piglet. This AA will show the highest fractional retention. Daily milk yield and composition were determined weekly over a 34-day lactation period. Within each litter, one piglet at birth and four piglets on d 35 of life were slaughtered. The protein content of the IB sow milk was similar to that reported for conventional breeds. However, branched-chain AA, Thr, Pro, Asp and Ala were in concentrations somewhat below the range of literature values and Arg and Met, substantially above it. Milk intake per piglet tended to be greater in Trial 2 (832 vs. 893 g/day respectively; p = 0.066). However, the IB piglets grew at 168 ± 3.3 g/day, irrespective of the trial. The whole-body protein of piglets at weaning and the protein deposited in their body during the lactating period showed very close AA pattern. Among EAA, His and Arg show the highest fractional retentions (g AA retained/g AA ingested) in whole-body tissues (1.019 ± 0.025 and 0.913 ± 0.017 respectively) and also the highest body to milk ratios (1.50 and 1.41 respectively). Gly and Ala presented, among non essential AA, the highest efficiencies of utilization for tissue deposition (1.803 ± 0.057 and 1.375 ± 0.026 respectively) and body to milk ratios (2.75 and 2.12 respectively). These results suggest that the low efficiency of utilization of milk protein and the low rate of gain of the IB suckling piglet can be explained by a marked shortage in His supply, in addition to the suboptimal milk provision of Arg, Gly and Ala.

Production and composition of Iberian sow's milk and use of milk nutrients by the suckling Iberian piglet.

Sixteen purebred Iberian (IB) sows were used in two consecutive trials to determine the efficiency of conversion of sow's milk into piglet body weight (BW) gain and the relationship between milk protein and body protein retention and between milk energy yield and body energy retention in the nursing IB piglet. In each trial, four sows were selected in order to evaluate their milk production, litter growth and nutrient balance measurements, together with four additional sows for milk sampling. Litter size was equalized to six piglets. Daily milk yield (MY) was determined weekly by the weigh-suckle-weigh technique over a 34-day lactation period. Piglets were weighed individually at birth and then weekly from day 5 of lactation. Milk samples were collected on days 5, 12, 19, 26 and 34 post partum. The comparative slaughter procedure was used to determine piglet nutrient and energy retention. One piglet from each litter was slaughtered at birth and four on the morning of day 35. Total MY was on average 5.175 ± 0.157 kg/day. The average chemical composition (g/kg) of the milk was 179 ± 4 dry matter, 53.4 ± 1.0 CP, 58.5 ± 3.8 fat, 10.4 ± 0.3 ash and 56.9 ± 2.3 lactose. Milk gross energy (GE) was 4.626 ± 0.145 MJ/kg. Milk intake per piglet tended to increase in trial 2 (832 v. 893 g/day; P = 0.066). Piglet BW gain contained (g/kg) 172.1 ± 1.3 protein, 151.5 ± 3.5 fat, 41.4 ± 0.6 ash and 635 ± 3 water and 10.127 ± 0.126 MJ GE/kg. Throughout the 34-day nursing period, the piglets grew at an average rate of 168 ± 3 g/day. The ratio of daily piglet BW gain to daily MY was 0.195 ± 0.002 g/g and the gain per MJ milk GE intake was 41.9 ± 0.5 g/MJ. The overall efficiency of protein accretion (g CP gain/g CP milk intake) was low and declined in trial 2 (0.619 v. 0.571; P = 0.016). Nutrient and energy deposition between birth and weaning were 27.4 ± 0.5 g/day protein, 24.2 ± 0.8 g/day fat and 1615 ± 40 kJ/day energy. Piglet energy requirements for maintenance were 404 kJ metabolizable energy (ME)/kg BW0.75. ME was used for growth with a net efficiency of 0.584. These results suggest that poor efficiency in the use of sow's milk nutrients rather than a shortage in milk nutrient supply might explain the low growth rate of the suckling IB piglet.