Effects of dietary protein content on milk composition of mixed parity lactating sows in a tropical humid climate

Eighteen multiparous Large White sows were used to determine the effects of dietary protein content andlactation stage on milk composition during a 28-d lactation under humid tropical climatic conditions. This study was conducted at the INRA facilities in Guadeloupe, French West Indies (latitude 16°N, longitude 61°W). The average minimum and maximum ambient temperatures and average daily relative humidity during the trial were 22.7 and 29.4°C, and 93.7%, respectively. The dietary experimental treatments were a normal protein (NP, 17.3%) diet and a low protein (LP, 14.1%) diet supplemented with essential amino acids. The ADFI tended to be higher for the sows fed the LP diets when compared with the NP treatment (i.e., +9%, P<0.10). Litter BW gain and mean BW of piglets at weaning were not affected by dietary protein level (P>0.10). The treatments did not influence (P>0.10) sow body weight loss during lactation. The sows fed LP diets tended to show lower backfat thickness losses when compared to the sows fed NP diets (2.4 vs. 6.3 mm, respectively; P<0.10). Milk production and composition were not affected by dietary treatments (P>0.10). Milk dry matter and ash contents linearly increased according to lactation stage (17.6 to 19.9%, and 0.72 vs. 97%, respectively from d 7 to d 27; P<0.01). Lactose content increased from d 7 to d 14 (3.95 vs. 4.91; P<0.01) and thereafter remained constant. Fat content did not change during lactation and averaged 7.5%. The amino acid concentrations in milk protein were affected by the lactation stage: methionine, threonine, tryptophan, valine, and alanine concentrations decreased (P<0.05) but glycine and glutamic acid contents increased (P<0.05) from d 7 to d 27. Fatty acids milk profile was not influenced (P>0.10) by lactation stage. Maternal BW loss during lactation was negatively correlated with the average daily feed intake (r=-0.76; P<0.05) and positively correlated with backfat thickness loss (r=0.55; P<0.05). A positive correlation between milk production and body reserves mobilisation (r=0.82; P<0.05) was also observed. Polyunsaturated fatty acid content in milk fat was positively correlated with ADFI and negatively correlated to maternal BW loss (r=0.62 and r=-0.60; P<0.05). In conclusion, reducing dietary protein content can be an alternative to attenuate the negative effects of heat stress by increasing ADFI. Milk composition changes significantly according to lactation stage and the ability of sows to produce milk will depend on their capacity to mobilize body reserve for providing milk precursors.