Partial suckling of lambs reduced the linoleic and conjugated linoleic acid contents of marketable milk in Chios ewes

Abstract

The objective of this work was to investigate the effect of weaning systems applied in a commercial dairy sheep farm on the fatty acid (FA) composition of marketable milk produced. Forty second parity, purebred Chios ewes were allocated to the following weaning treatments: (a) ewes were weaned from their lambs at 48h after birth and machine milked twice daily [no lambs (NL) group, n=20]; or, (b) starting 48h postpartum, ewes were separated from their lambs for 12h during the evening, machine milked once daily the following morning, and lambs were allowed to suckle for 12h during the day for the first 5wk of lactation [partial suckling (PS) group, n=20]. After weaning of the PS lambs at wk 6 of age, all ewes were machine milked twice daily. Commercial milk yield and milk composition was recorded weekly (fat, protein, FA content) or fortnightly (somatic cell counts) throughout the first 10wk of lactation. The PS ewes compared with NL group produced commercial milk lower in milk yield, milk fat, and somatic cell counts, but not in protein content during the first 5-wk period. Such differences were not observed after weaning of the PS lambs. The FA profile of commercial milk was also affected by partial suckling during the preweaning period. Total polyunsaturated FA were higher in NL compared with PS ewe milk at wk 1, 2, 4, and 5 (on average, 21% higher), whereas no differences were detected between NL and PS ewe milk from wk 6 to 10 of lactation. From the polyunsaturated FA, linoleic acid (C18:2 cis-9,cis-12) and conjugated linoleic acid (C18:2 cis-9,trans-11; rumenic acid) were particularly affected, showing on average a reduction of 18 and 38%, respectively. From the monounsaturated FA, vaccenic acid (C18:1 trans-11) was affected during wk 1 and 2 of the treatment period, with the PS ewe milk having reduced content compared with the NL milk. Other unsaturated FA, such as oleic acid and α-linolenic acid, or saturated FA were not found to be affected by the weaning treatment. The results indicate that partial suckling of lambs during the first 5wk of lactation adversely affected both the total fat content of milk obtained by machine milking of their dams and the unsaturation content of the milk fat. Particularly affected were the linoleic acid and cis-9,trans-11 conjugated linoleic acid content of ewe milk.