The evaluation of fat to protein ratio in milk as an indicator of calving to conception interval in dairy cows using various biostatistical methods

Effect of different dry period duration on milk components and serum metabolites, and their associations with the first conception rate in multiparous Holstein dairy cows

The aims of the present study were to evaluate the effects of different dry period (DP) lengths on milk fat to protein ratio (FPR) and metabolic status – blood leptin, adiponectin and non-esterified fatty acids (NEFA) concentrations in dairy cows, and their associations with the result of the first timed artificial insemination (TAI). Cows were blocked either to short DP (SDP; 30±2 days; n=72) or conventional DP (CDP; 60±2 days; n=76). Milk FPR was calculated at 30 and 60 days in milk (DIM). Body condition score (BCS) was recorded at –60, –30, calving, and 60 DIM. Blood samples were obtained at –60, –30, –7, calving, +7, +30, and +60 DIM for serum metabolites measurement. TAI was implemented between 65–75 DIM for all cows. Milk FPR and its changes were statistically analysed using an independent sample t test. To assess the impact of time, the pattern of BCS, and serum metabolites on the result of the first AI, repeated measure ANOVA was used. Only FPR-30 DIM revealed significant difference between pregnant and non-pregnant cows in SDP group (P<0.01). Reduced BCS loss was observed in the SDP group and followed by slightly higher probability of pregnancy at first AI (P=0.19). Leptin was not altered by shortening the DP (P≥0.1). Significant differences were observed in blood adiponectin prepartum (P<0.001) and at +7 DIM (P<0.01), as well as in NEFA at +7 and +30 DIM between the two groups (P<0.05). Pregnant cows following the first AI had significantly high postpartum leptin concentrations (P<0.05), high prepartum adiponectin (P≤0.001), and lower NEFA at +7 DIM (P<0.01) in the SDP group. In conclusion, shortening the dry period caused reduced BCS loss postpartum and variations in serum metabolits that favoured the possibility of pregnancy at first AI.

Associations between milk fat, protein and fat-to-protein ratio with some reproductive indices in dairy cows

Postpartum induced lipolysis by negative energy balance (NEB) causing an increase in milk fat, a decrease in milk protein, and as a consequence an increase in milk fat to protein ratio (FPR). The aim of this study was to evaluate the relationship between milk FPR and first service conception risk (FSCR), days to first service (DFS) and calving to conception interval at first service (CCIFS). Therefore, milk and reproduction data of 1,375 primiparous and multiparous Holstein dairy cows from 10 commercial dairy farms located on sub-tropical region were collected on days 30 and 60 of days in milk (DIM) and near the first service. The Pearson correlation test of milk compositions revealed only a significant correlation between milk protein at day 30 DIM and DFS, but in Logistic regression analysis it did not have a constant effect on reproductive indices. On the other hand, the effect of previous dry-off duration and AI season on FSCR were significant. Based on the result of the present study, it is concluded that milk compositions such as fat, protein and FPR had no correlation with the result of the first AI.