Nucleotides in sow colostrum and milk at different stages of lactation1,2,3

An experiment was conducted with the objective of measuring the concentrations of total milk solids (TMS), CP, and 5′monophosphate nucleotides in sow colostrum and milk. Twelve multiparous sows (Landrace × Yorkshire × Duroc) were used. Litter size was standardized at 11 piglets for all sows at farrowing. Sows were fed an 18.45% CP corn–soybean meal-based diet throughout lactation. The experimental period was the initial 28 d of lactation, with colostrum collected within 12 h of farrowing and milk collected on d 3, 7, 14, 21, and 28. Colostrum and milk samples were analyzed for TMS, CP, adenosine 5′monophosphate (5′AMP), cytidine 5′monophosphate (5′CMP), guanosine 5′monophosphate (5′GMP), inosine 5′monophosphate (5′IMP), and uridine 5′monophosphate (5′UMP). Total milk solids decreased (P < 0.05) from 26.7% on d 0 to 23.1% on d 3. The TMS further decreased (P < 0.05) to 19.3% on d 7, but remained relatively constant thereafter at 18.2, 18.8, and 19.2% on d 14, 21, and 28, respectively. The concentration of CP decreased from 16.6% in colostrum to 7.7, 6.2, 5.5, 5.7, and 6.3% in milk collected on d 3, 7, 14, 21, and 28, respectively (linear and quadratic effect; P < 0.05). Concentrations of 5′AMP, 5′CMP, 5′GMP, and 5′IMP increased from d 0 to d 3 and d 7, and then decreased during the remaining lactation period (quadratic effect; P < 0.05). The concentration of 5′UMP decreased from d 0 to 28 of lactation (linear and quadratic effects; P < 0.05). In colostrum, 5′UMP represented 98% of all 5′monophosphate nucleotides, and in milk, 5′UMP accounted for 86 to 90% of all nucleotides, regardless of day of lactation. The results of this experiment suggest that the concentrations of TMS and CP in sow mammary secretions changed during the first week of lactation, but were constant thereafter. Likewise, the concentrations of 5′monophosphate nucleotides changed during the initial week postpartum, but during the last 2 wk of a 4-wk lactation period, the concentrations were constant.