Changes of milk fat, crude protein, NPN and protein: fat ratio in holstein cows fed a high concentrate diet from early to late lactation

Percentages and yields of fat, crude protein [CP], true protein [TP] and non-protein nitrogen [NPN] were assessed in milk of four groups of Holstein cows, at early, mid and late lactation [days in milk 20-70, 71-110. 111-150 and 151-210], on a diet rich in concentrates during a hot summer. Four milk samples were taken from individual cows at 10-day intervals. Milk fat percentages were close to breed average and increased toward the end of lactation with a tendency [P = 0.055] for significant difference between the early and late lactation. Percentages of CP [P = 0.14] and TP [P = 0.478], however, were low similarly among all groups and did not follow the normal pattern of the breed. Percentage of NPN was significantly higher in groups Ill and IV [P = 0.005]. Yields of fat [P = 0.035], CP [P = 0.002] and TP [P = 0.001], but not NPN [P = 0.589], decreased toward the end of lactation. There was a negative correlation [r = -0.354, P<0.001] between the percentages of NPN and TP. However, no correlation was observed between the percentages of NPN and CP. Despite a very strong correlation between yields of CP and TP [r = 0.983, P<0.001], the correlation between the yield of CP and that of NPN was much weaker [r = 0.473, P<0.001]. It is concluded that percents and yields of milk fat, close to breed average are attainable at any stage of lactation on high concentrate diets in hot weather. However, regarding milk protein, cows may not perform well. TP may be more affected than CP

Changes in and correlations between some serum constituents and milk components from early to late lactation in a dairy herd with subclinical production disorders

Changes in some serum constituents and milk components and correlations between them, were used for defining the reason [s] of suboptimal milk composition in a dairy herd with a history of low protein tests during summers. Four groups of 8 adult Holsteins, 20-70, 70-110, 110-150 and 150-210 days in milk [DIM], under heat stress, with similar feeding and management practices were sampled for blood and milk four times on a 10 day interval. Milk volume, percentages of milk fat and protein and levels of serum glucose, total protein, albumin and BUN were determined. Milk volume decreased as DIM increased [P<0.05]. Milk fat showed normal changes, but milk protein was similarly low in all groups [P>0.05], showing probable shortages in energy and/or protein intake. Serum parameters showed no significant differences among groups [P>0.05]. Weak positive correlations were found between serum total protein and milk components after 150 DIM [maximum correlation with milk fat, r = 0.61]. It is concluded that shortage in intake of energy and/or protein, which may result in lowered milk protein, may not be differentiated by measuring serum glucose, total protein, albumin and BUN and milk components. More detailed experiments on serum and milk are necessary for defining the problem properly