Morphological quality of oocytes and blood plasma metabolites in repeat breeding and early lactation dairy cows.

The objectives of the study were to evaluate the morphological quality of oocytes in repeat breeder and early lactation cows and to determine the possible associations between the quality of oocytes and a range of blood metabolites. Oocyte quality and a range of metabolites were compared between 29 repeat breeder and 13 early lactation cows. The yield of oocytes from the repeat breeders was lower than that from the early lactation cows (4.4 ± 0.2 vs 5.4 ± 0.6, p < 0.05). Percentages of abnormal oocytes for the repeat breeders and the early lactation cows were 52.5% and 37.9%, respectively (p < 0.001). An excess of abnormal oocytes to normal was found in 55.2% of the studied repeat breeders (65.8% vs 34.2%, p < 0.05). Total protein, glucose and aspartate aminotransferase did not differ (p > 0.05) between the repeat breeders with an excess of abnormal oocytes (81 ± 1.0 g/l, 3.5 ± 1.0 mmol/l and 68.5 ± 3.7 U/l), those with the prevalence of normal oocytes (84 ± 1.0 g/l, 3.6 ± 0.1 mmol/l and 73.2 ± 3.5 U/l) and the early lactation cows (83 ± 2.0 g/l, 3.7 ± 0.1 mmol/l and 74.5 ± 3.6 U/I). The repeat breeders with an excess of abnormal oocytes had higher (p < 0.05) urea (5.2 ± 0.2 mmol/l) level than in those with the prevalence of normal oocytes (4.8 ± 0.2 mmol/l) and the early lactation cows (4.7 ± 0.2 mmol/l). A trend for higher total cholesterol and lactate dehydrogenase activity was found in the repeat breeders with an excess of abnormal oocytes. In conclusion, it is suggested that possible causes of repeat breeding in dairy cows may include impaired oocytes. An excess of abnormal oocytes in the repeat breeder cows was associated with elevated blood plasma levels of urea.

Thyroxine, triiodothyronine and reverse-triiodothyronine concentrations in blood plasma in relation to lactational stage, milk yield, energy and dietary protein intake in Estonian dairy cows.

Average levels of thyroxine (T4), triiodothyronine (T3) and reverse-triiodothyronine (rT3) in blood plasma of 159 Estonian Red and Estonian Black and White cows were 55.2 nmol/L, 1.78 nmol/L and 0.25 nmol/L respectively. Animals were grouped according to stage of lactation. The T4 level was significantly lower during the early stage of lactation (45.1 nmol/L), compared with later stages, but increased as the stage of lactation progressed (late stage of lactation - 56.7, dry cows 64.3 nmol/L). The T3 level was significantly higher at the late stage of lactation (1.93 nmol/L) compared with the early stage of lactation (1.71 nmol/L) and level in dry cows (1.71 nmol/L). rT3 showed a trend similar to that found for T4 (lowest plasma concentration in early lactation, 0.19; highest in the dry period, 0.33; late lactation, 0.24 nmol/L). Levels of all thyroid hormones were negatively related to the daily milk yield (T4-r = -.51, rT3-r = -.47, calculated thyroid index as rT3 x T3 x T4-r = -.52, for all p < .0001; T3-r = -.32, p < .01). Plasma thyroid hormone concentrations were affected by energy and dietary protein intake. Differences were found in thyroid hormone levels between the 2 breeds and between summer and winter holding periods for Estonian Red cows, which could all be explained by differences in the feeding level and daily milk yield. It is suggested that maintaining low levels of thyroid hormones in early lactation may be one of the dairy cow's mechanisms of reducing metabolic demand.