Triiodothyronine and thyroxine during gestation in dairy cattle selected for high and low milk production

Maintenance energy requirements of beef cows and relationship with cow and calf performance, metabolic hormones, and functional proteins

Gestating Angus, nonlactating, spring-calving cows were used to determine variation in maintenance energy requirements (MR); to evaluate the relationship among MR and cow and calf performance, plasma concentrations of IGF-I, T4, glucose, insulin, and ruminal temperature; and to describe the LM proteome and evaluate protein abundance in cows with different MR. Cows (4 to 7 yr of age) with a BCS of 5.0 ± 0.2 and BW of 582 ± 37 kg in the second to third trimester of gestation were studied in 3 trials (trial 1, n = 23; trial 2, n = 32; trial 3, n = 38). Cows were individually fed a complete diet in amounts to meet predicted MR (Level 1 Model of NRC), and feed intake was adjusted weekly until constant BW was achieved for at least 21 d (maintenance). Cows were classified on the basis of MR as low (>0.5 SD less than mean, LMR), moderate (±0.5 SD of mean, MMR), or high (>0.5 SD more than mean, HMR) MR. Blood samples were taken at maintenance and at 2 mo postpartum in trial 2. Muscle biopsies were taken from LMR and HMR after cows consumed actual MR for 28 d (trial 2) or 21 d (trial 3). Proteins from LM were separated by 2-dimensional difference gel electrophoresis and were identified, and abundance was quantified and compared. The greatest differences in MR between cows were 29%, 24%, and 25% in trials 1, 2, and 3, respectively. Daily MR (NEm, kcal·BW(-0.75)·d(-1)) averaged 89.2 ± 6.3, 93.0 ± 4.9, and 90.4 ± 4.6 in trials 1, 2, and 3, respectively. Postpartum BW and BCS, calf birth and weaning weights, postpartum luteal activity, and ruminal temperature were not influenced by MR of the cows. Concentrations of IGF-I were greater (P = 0.001) in plasma of MMR compared with LMR cows consuming predicted MR diets, and MR was negatively correlated with concentrations of IGF-I in plasma (r = -0.38; P = 0.05) at 2 mo postpartum. A total of 103 proteins were isolated from LM; 52 gene products were identified. Abundance of specific proteins in the LM was not influenced (P > 0.11) by MR. Variation in MR of cows will make it possible to improve feed efficiency by selection. Identification of biomarkers for MR will allow selection of more efficient cows, which consume less feed and produce calves with similar weaning weights. Productive cows that require less feed for maintenance will improve efficiency of production and enhance sustainability of the environment.

Validation and Application of an Immunofluorimetric Assay for Detection of Serum Free Triiodothyronine and Free Thyroxine Concentrations in Buffalo (Bubalus Bubalis) under Various Physiological Conditions

The current study was designed to validate an immunofluorimetric method to measure free triiodothyronine (fT3) and free thyroxine (fT4) concentrations in the serum of buffalo and to develop a better understanding of thyroid metabolism in buffalo ( Bubalus bubalis) of different ages and reproductive statuses. Free triiodothyronine and fT4 were determined in sera from 4 groups of 10 animals, each representing 5–10-year-old lactating buffalo, 2–3–year-old first calf heifers, 1–1.5-year-old virgin heifers, and 5–10–year-old dry buffalo. The average sensitivity of the immunofluorimetric assay was 5.9 pmol/l for fT3 and 14.7 pmol/l for fT4. Intra-assay and interassay coefficients of variation were 5.6% and 5.1% for fT3 and 1.5% and 4.3% for fT4, respectively. Virgin heifers had higher average values for fT3 and fT4, while lactating buffalo had the lowest average values. Dry buffalo and first calf heifers had intermediate fT3 and fT4 values. The findings of this study suggested that lactating buffalo were in a state of low thyroid activity, while virgin heifers had increased thyroid activity.

5'-deiodinase activity and circulating thyronines in lactating cows

To investigate the correlation between lactation and thyroid hormone metabolism, the authors studied concentrations of total and free thyroxine (T4 and fT4), triiodothyronine (T3 and fT3), and reverse triiodothyronine (rT3) in plasma and milk, as well as liver and mammary gland 5'-deiodinase (5'D) activity in dry, early, middle, and late lactating dairy cows. Cows in early lactation show lower plasma levels of T4 and rT3 than dry, middle, and late lactating animals, whereas T3 shows the lowest plasma levels in the dry period; free T4 and T3 show a similar pattern. In early lactation there is a clear decrease in liver 5'D associated with a notable increase in mammary 5'D. Concentrations of T4 and T3 in milk drop significantly in the first few days after delivery, whereas rT3 increases up to the fourth month. The findings suggest a relationship between the hypothyroid status of lactating cows and the rearrangement of organ-specific 5'-deiodinase activity related to the maintenance of the udder's function.

Effect of lactational intensity on extrathyroidal 5'-deiodinase activity in rats

Concentrations of thyroxine and triiodothyronine in serum and 5'-monodeiodination activity in liver and kidney were studied in lactating Sprague-Dawley rats with different litter sizes. Litter sizes were adjusted at birth to 0 (postpartum nonlactating group), 4, 8, 12, and 16 pups per lactating rat. Serum and tissue samples were collected from lactating rats and pups on d 12 of lactation and from 6 nulliparous females. Nulliparous and postpartum nonlactating rats did not differ in serum thyroxine, triiodothyronine concentrations, or in 5'-deiodinase activity in liver and kidney. As litter size increased, maternal serum thyroxine, triiodothyronine concentrations, and 5'-deiodinase activity in liver and kidney decreased. Growth rate of pups was inversely correlated with litter size and positively correlated with concentration of serum thyroxine and liver 5'-deiodinase in mothers. In pups, serum triiodothyronine concentrations decreased as litter size increased, but serum thyroxine concentrations were not affected. Results suggest a relationship between the hypothyroid status of lactating rats and suckling intensity. The thyroid status of the dam may influence thyroid status and growth of offspring.

Levels of T4, T3 and cortisol in the blood serum of the European bison (Bison bonasus) in the winter period

1. In the blood of 56 European bison, the levels of T4, T3, and the ratio of T3:T4 and cortisol were studied. 2. Between December and March, the T4 level changed from about 53 to 83 ng/ml of blood serum but in April it increased to 90 ng/ml. 3. The level of T3 in this period was 0.817-1.475 ng/ml and in April it was 2.40-3.40 ng/ml. 4. The ratio of T3:T4 was 0.015-0.024 and in April it increased to 0.027-0.052. 5. The level of cortisol changed from 1.00 to 6.70 ng/ml and in April it was from 1.00 to 14.00 ng/ml.

Somatotropin and lactation

Somatotropin, which can now be produced by biotechnology, could have an enormous impact on the dairy industry. Milk yield has been increased up to 40% with daily injections of somatotropin. Cows adjust their nutrient intake to support this increase. Somatotropin does not adversely affect cows' health, although all studies to date have been for less than one complete lactation. The search for a single biochemical or physiological event to account for the effects of somatotropin on milk production is elusive. Coordinated changes in many tissues and physiological processes occur to support the increases in the synthesis of lactose, fat, and protein in the mammary gland. Changes in the irreversible loss and oxidation rates of two key metabolites, glucose and free fatty acids, can quantitatively account for increases in lactose and milk fat during the short-term administration of somatotropin. Similarly, feed intake and live weight changes can account for increases in milk production in the longer experiments. Parallels between physiological changes that occur during somatotropin administration and differences between genetically high and lower yielding cows are highlighted, and the rates of improvement that can be expected from various new technologies are quantified. Existing data on the safety of somatotropin to both the consumer and the animal are evaluated.