Effects of divergent Holstein-Friesian strain and diet on diurnal patterns of plasma metabolites and hormones.

Commonly measured metabolite and hormone concentrations used to describe the metabolic status of lactating cows undergo diurnal variation resulting in distinct patterns. Studies have shown that feeding events can modulate these diurnal patterns as cows respond to the nutrient intake. What is less clear is the extent to which cow genetics and diet interact to modify the diurnal patterns of specific nutritionally related metabolites and hormones. The objective of this study was to investigate diurnal patterns in circulating metabolite and hormone concentrations in divergent strains of Holstein-Friesian cows (North American, NA; and New Zealand, NZ) offered either fresh pasture (FP) or a total mixed ration (TMR). Plasma concentrations of growth hormone (GH), insulin-like growth factor-1 (IGF-1), glucose, insulin, ß-hydroxybutyrate (BHBA), and non-esterified fatty acids (NEFA) were determined at 4-h intervals for a minimum of three consecutive days. All of the above metabolites and hormones exhibited within-day variability. Main effects of genetic strain and diet were observed for plasma IGF-1, and a strain by diet interaction was observed for GH. Time of day x diet interactions were observed for both glucose and insulin. Three-way interactions (time of day x diet x strain) were observed for BHBA and NEFA. These data indicate different levels of diurnal variation, with glucose, insulin, NEFA and BHBA having the largest daily variation. These diurnal patterns need to be considered in future investigations of these metabolites and hormones.

A compartmental model describing changes in progesterone concentrations during the oestrous cycle.

The objective of this study was to develop a mathematical model that accurately describes the rise and decline in plasma progesterone concentrations, and is able to define parameters describing progesterone appearance and disappearance during the bovine oestrous cycle. Daily plasma progesterone data from 27 cows were used to develop a compartmental model consisting of an appearance function and an appearance modulating function. Model outputs included an apparent appearance or secretion duration, appearance rate and an average disappearance rate (expressed as arbitrary units per day; units/d). Shape-based clustering identified three common shape-based groups (or clusters) of progesterone profiles defined as either 'peaked' profile, with the profile reaching a distinguishable peak, 'structured', with the profile exhibiting a wave-like pattern, or 'flat top', with the profile reaching a plateau. Differences in the model parameters for the three different shapes of progesterone profiles were examined: peaked (n=13), flat top (n=7) and structured (n=7). The mean duration of apparent appearance was 11.49 (SD 0.17 d) for all 27 profiles. The model estimates for total appearance of progesterone (area under the curve; ng/ml per cycle), mean appearance rate and maximum appearance rate were 69.04 ng/ml per cycle (SD 15.2 ng/ml per cycle), 3.19 ng/ml per cycle (sd 0.7 ng/ml per d) and 6.70 ng/ml (SD 1.31 ng/ml), respectively. The average disappearance rate was 1.0 units/d (SD 0.04 units/d). The apparent appearance duration was greatest (P<0.01) in the flat top profiles (12.54, SD 0.41 d) followed by the structured (11.77, SD 0.66 d) and the peaked (10.80, SD 0.30 d) profiles. Total and mean progesterone appearance, maximum progesterone appearance rate, and the progesterone disappearance rates were not different between the profiles. The model successfully simulated all components of the progesterone profile and was able to define specific parameters of different shaped progesterone profiles. A simple model able to estimate parameters describing progesterone appearance and disappearance can be used to explore the relationships between profile shapes and reproductive outcomes.

A comparison between feeding systems (pasture and TMR) and the effect of vitamin E supplementation on plasma and milk fatty acid profiles in dairy cows.

Unidentified constituents in fresh pasture increase milk fat cis-9, trans-11 conjugated linoleic acid (CLA) concentration, and prevent milk fat depression, even though ruminal conditions conducive to reducing milk fat synthesis exist. One possible explanation is vitamin E (kappa-tocopherol), a constituent high in fresh pasture, but naturally low in conserved/dried forages and cereal grains. Twenty late-lactating dairy cows previously consuming a total mixed ration (TMR) were randomly allocated to one of two dietary treatments for 21 d: TMR (control; n=10); and TMR plus an additional 10,000 i.u. alpha-tocopherol/d (VIT E; n = 10). These cows were simultaneously compared with 13 late-lactation dairy cows previously grazing fresh pasture (PAS) balanced for age, parity and genetic merit. Average daily alpha-tocopherol intakes were approximately 468, 10,520 and 1,590 i.u./cow for the control, VIT E and PAS treatments, respectively. Dietary alpha-tocopherol supplementation (VIT E v. control) slightly increased milk fat content by 0.23 percentage units, but did not significantly alter milk fatty acid composition. Plasma trans-11 18:1 (VA) content tended to increase and trans-10 18:1 levels numerically declined following alpha-tocopherol supplementation suggesting possible changes in rumen biohydrogenation products. In addition, increased alpha-tocopherol intake in TMR-fed cows decreased serum urea levels and tended to alter milk fat 15:0 suggesting changes in rumen microbial populations. However, when compared with cows grazing pasture, TMR-fed cows supplemented with alpha-tocopherol, still produced milk with lower cis-9, trans-11 CLA and VA, and higher trans-10 18:1 concentrations suggesting alpha-tocopherol is not a primary reason for milk fatty acid profile differences between pasture and TMR-fed cows. Therefore, additional unknown pasture constituents favour production of fatty acids originating from the cis-9, trans-11 instead of the trans-10, cis-12 CLA biohydrogenation pathways.

Nutritional limitations to increased production on pasture-based systems.

The constraints to high levels of milk production imposed by a high-quality-pasture diet, and development of feeding strategies to overcome these limitations, were examined by modelling the nutritional status of New Zealand Friesian and North American Holstein-Friesian dairy cows grazing high-quality pasture. The Cornell Net Carbohydrate and Protein System (CNCPS) was used to predict sensitivity of milk production to a 10% change in the composition of pasture nutrients. The rate at which fibre and protein were degraded in the rumen and the value given to effective fibre and lignin content significantly affected the supply of metabolisable energy and protein, and the profile of amino acid supply. The first limiting factor in milk production when only high-quality pasture was fed was metabolisable energy supply, while specific amino acids, particularly methionine and lysine, limited milk production when > 20 g/kg diet consisted of a grain supplement. Compared with cows fed a total mixed ration in confinement, North American Holstein-Friesians grazing all pasture produced less milk (29.6 v. 44.1 kg/d). Of the difference in milk production 61% could be attributed to a lower DM intake (19 kg/d v. 23.4 kg/d). Predictions using the CNCPS indicated that supply of metabolisable energy was the first-limiting factor for milk production from high-quality pasture (251 g crude protein (N x 6.25)/kg, 432 g neutral-detergent fibre/kg, 77% in vitro DM digestibility), rather than metabolisable protein or amino acids. In addition, these nutritional limitations imposed by pasture diets will be greater for dairy cow genotypes that have not been selected for high performance within a pasture system.

Fecal glucocorticoid metabolites as a measure of adrenal activity in dairy cattle.

The feasibility of monitoring acute adrenal activity in New Zealand dairy cattle by measuring fecal glucocorticoid metabolites was investigated. Fecal glucocorticoid measurement has potential as an indicator of adrenal activity and animal stress because sampling is relatively noninvasive, does not interfere with the stress response itself, and permits on-farm monitoring. Fecal samples were collected from dairy cattle following ACTH challenge and exposure to stressors (novel environment, transport). Two immunoassays (11,17-dioxoandrostane enzymeimmunoassay and ICN corticosterone radioimmunoassay) were compared. Both assays detected increased immunoreactive fecal glucocorticoid metabolites following acute adrenal activity and the temporal relationship between plasma corticosteroids and fecal metabolite excretion was determined. The time to peak excretion was closely related to the transit time of digesta passing between the bile duct and the rectum and was affected by seasonal changes in feed intake and pasture digestibility. We conclude that measurement of glucocorticoid metabolites reliably indicates acute adrenal activity in dairy cattle and in combination with other physiological and behavioral measures has potential for monitoring health and welfare in dairy cattle. (c) 2002 Elsevier Science (USA).