Search

The bovine CSN1AG allele is associated with a lower proportion of alpha s1-casein in milk and is characterized by an insertion in the last noncoding exon (19th). According to DNA sequence analysis, the location, length, and origin of the insertion characterizing the bovine CSN1AG allele have been identified. This insertion interrupts the 19th exon between nucleotides 58 and 59, is 371 bp long, and has a high level of homology with relicts of long interspersed elements of retropositional origin. Northern blot analysis shows that the inserted element is transcribed and that the number of transcripts of the CSN1AG allele is less than one-half of the number of transcripts of the CSN1AB allele. The lower amount of alpha s1-casein in milk obtained from cows carrying the CSN1AG allele can be explained by a reduced mRNA stability. Furthermore, a method has been developed using polymerase chain reaction for identification of the carriers of the CSN1AG allele.

This study evaluated the effects of recombinant bovine somatotropin (bST; one injection of 320 mg per ewe) on milk production and composition and on the grazing behavior of multiparous ewes in the third to fourth lactation. Forty Comisana lactating ewes were divided into four groups: 1) untreated, grazing on natural pasture (botanical composition: 35% of Graminaceae, 49% of Fabaceae, 6% of Cruciferae, 10% of other families) at a low stocking rate (16 m2/d); 2) untreated, grazing at a high stocking rate (8 m2/d); 3) treated with bST, grazing at a low stocking rate; and 4) treated with bST, grazing at a high stocking rate. The diets of the ewes were supplemented with vetch and oat hay (500 g/d) and with concentrate (500 g/d). Treatment increased milk production (923.8 vs. 669.5 g/d) but had little effect on fat and protein contents. Administration of bST significantly increased herbage intake; the effect on intake was more marked at the high stocking rate. Under these grazing conditions, the treated ewes reduced selective intake behavior and, thus, achieved good feed intake despite the low biomass availability.