Phenotypic population screen identifies a new mutation in bovine DGAT1 responsible for unsaturated milk fat.

Selective breeding has strongly reduced the genetic diversity in livestock species, and contemporary breeding practices exclude potentially beneficial rare genetic variation from the future gene pool. Here we test whether important traits arising by new mutations can be identified and rescued in highly selected populations. We screened milks from 2.5 million cows to identify an exceptional individual which produced milk with reduced saturated fat content, and improved unsaturated and omega-3 fatty acid concentrations. The milk traits were transmitted dominantly to her offspring, and genetic mapping and genome sequencing revealed a new mutation in a previously unknown splice enhancer of the DGAT1 gene. Homozygous carriers show features of human diarrheal disorders, and may be useful for the development of therapeutic strategies. Our study demonstrates that high-throughput phenotypic screening can uncover rich genetic diversity even in inbred populations, and introduces a novel strategy to develop novel milks with improved nutritional properties.

Genetic ancestry modifies fatty acid concentrations in different adipose tissue depots and milk fat.

The objective of this study was to determine the effect of cow genetic strain on fatty acid (FA) profiles in adipose tissue and milk. Adipose samples from two subcutaneous (shoulder and tail-head) and three visceral (kidney channel, mesenteric and omental) depots were obtained post mortem from New Zealand (NZ; n = 8) and North American (NA; n = 8) Holstein-Friesian cows. At the time of slaughter cows were in similar body condition (NZ: 4.0 ± 0.03, NA: 4.0 ± 0.02; ± SD) and stage of lactation (NZ: 90 ± 11.2 d; NA: 83 ± 4.3 d; ± SD). Milk was collected during the a.m. milking prior to slaughter and milk fat was extracted. Adipose and milk fat FA were quantified using gas chromatography. NZ cows had a lower proportion of saturated FA in shoulder, tail-head and omental adipose tissue and a greater proportion of mono-unsaturated FA and an elevated Δ9-desaturase index in shoulder and tail-head adipose tissue. The proportions of individual FA differed between adipose depots, with proportions of de-novo FA greater in subcutaneous compared with visceral adipose depots. Milk from NZ cows contained greater concentrations of short chain FA (C8 : 0-12 : 0) and CLA, and less cis-9 18 : 1 than milk from NA cows. Regression analysis identified moderate associations between milk FA and shoulder adipose tissue FA for 18 : 2 (R(2) = 0.24), 18 : 3 n - 3 (R(2) = 0.39), and polyunsaturated fatty acids (R(2) = 0.38). Results from this study support the hypothesis that genetic strain dictates FA profiles in adipose tissue and milk and may alter the metabolic status of the various adipose depots differently. The data further support the premise that genetic strain affects the metabolic status of the various adipose depots differently. Elucidating the mechanisms that regulate the different adipose depots in the NZ and NA strains will increase our understanding of tissue mobilization and replenishment.

The effect of temperament and responsiveness towards humans on the behavior, physiology and milk production of multi-parous dairy cows in a familiar and novel milking environment.

The objectives of this study were to investigate whether; 1) temperament or 2) behavioral responsiveness to humans, can affect the behavior, physiology and productivity of dairy cows being milked in a familiar and novel milking environment. Temperament of multi-parous cows was defined based on exit time from a restraint device, as High Responders (HR; n=10), Medium Responders (MR; n=10) or Low Responders (LR; n=10). The behavioral response of cows to humans was assessed using four tests: restraint, exit speed, avoidance distance test and a voluntary approach test. Cows were milked according to their established routines in a rotary (familiar) milking parlor and behavioral, physiological and production data were collected over five consecutive days, including heart rate, cortisol and oxytocin concentrations and milk yield. The following week, cows were milked in a novel environment (herringbone parlor within the same farm facility) over five consecutive days, and the data and sample collection program was repeated. Cows were then given an exogenous adrenocorticotropic hormone (ACTH) challenge to measure adrenal responsiveness. Exit time was negatively correlated with the behavioral responses of cows to restraint and human avoidance distance (HAD) in the paddock and arena. The behavioral response of cows to the milking process was greater in MR than LR and HR cows in the familiar and novel milking environments. Milk yields were greater in LR than HR cows in the novel but not the familiar milking parlor. Oxytocin concentrations increased during milking in the novel environment, regardless of cow temperament. In the familiar and novel environments, heart rates were higher in HR than LR cows before and during milking and rMSSD was lower in HR cows during milking in a novel environment. There was no difference in cortisol concentrations between LR and HR cows in response to an ACTH challenge, but HR cows had higher baseline cortisol levels than LR cows. The number of leg lifts cows performed when restrained in the crush was associated with several physiological and milk production measures. These results indicate that cows with different temperaments vary in their basal physiology as well as their behavioral and physiological responses to milking and stress associated with being milked in a novel environment.

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.

Pasture-based dairying: challenges and rewards for New Zealand producers.

New Zealand dairying farm systems are principally pasture-based or seasonal supply. Features of these systems and their management are described, together with their advantages and limitations. The characteristics of reproductive management needed to attain satisfactory economic performance of these farm systems is discussed. The low-cost pasture-based seasonal system dictates that animals be bred over a very short period compared to many overseas countries and this is assisted in particular by the use of hormonal treatment for anoestrum. Oestrus synchrony is not widely used although uptake is increasing, particularly in large herds. The constraints imposed by the farming system represent a significant challenge to the application of embryo technologies as embryos must be recovered and transferred over the short period between calving and artificial insemination and farmers demand either a high pregnancy rate or a high value calf to compensate for the cost of the procedure and any delay in achieving a pregnancy.

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).