In Westernized societies, average consumption of n-6 polyunsaturated fatty acids (PUFAs) far exceeds nutritional requirements. The ratio of n-6 to n-

Most dairy cows suffer uterine microbial contamination postpartum. Persistent endometritis often develops, associated with reduced fertility. We used a model of differential feeding and milking regimes to produce cows in differing negative energy balance status in early lactation (mild or severe, MNEB or SNEB). Blood hematology was assessed preslaughter at 2 wk postpartum. RNA expression in endometrial samples was compared using bovine Affymetrix arrays. Data were mapped using Ingenuity Pathway Analysis. Circulating concentrations of IGF-I remained lower in the SNEB group, whereas blood nonesterified fatty acid and β-hydroxybutyrate concentrations were raised. White blood cell count and lymphocyte number were reduced in SNEB cows. Array analysis of endometrial samples identified 274 differentially expressed probes representing 197 recognized genes between the energy balance groups. The main canonical pathways affected related to immunological and inflammatory disease and connective tissue disorders. Inflammatory response genes with major upregulation in SNEB cows included matrix metalloproteinases, chemokines, cytokines, and calgranulins. Expression of several interferon-inducible genes including ISG20, IFIH1, MX1, and MX2 were also significantly increased in the SNEB cows. These results provide evidence that cows in SNEB were still undergoing an active uterine inflammatory response 2 wk postpartum, whereas MNEB cows had more fully recovered from their energy deficit, with their endometrium reaching a more advanced stage of repair. SNEB may therefore prevent cows from mounting an effective immune response to the microbial challenge experienced after calving, prolonging the time required for uterine recovery and compromising subsequent fertility.

Alteration of the polyunsaturated fatty acid (PUFA) composition of milk by dietary supplementation of cows may be beneficial to human health. However, dietary PUFAs may influence synthesis of both prostaglandins and steroid hormones. This study examined the effects of dietary PUFAs on reproductive parameters in lactating cows. Cows were fed an isoenergetic control ration (n = 8) or a diet supplemented with LinPreme (n = 7) or SoyPreme (n = 8). These proprietary feeds are derived from linseed or soybeans and contain high concentrations of linolenic acid (LNA, n-3) or linoleic acid (LA, n-6) protected PUFA, respectively. Both PUFA-supplemented diets reduced plasma progesterone, particularly in the early luteal phase, and increased the number of medium-sized (5-10 mm in diameter) follicles. The diameter of the first dominant follicle, insulin-like growth factor I (IGF-I) concentrations at oestrus and cholesterol concentrations were all higher in cows fed a diet supplemented with LA (n-6) than in cows that did not receive this supplement. In cows fed a diet supplemented with LNA (n-3), there was an increase in oestradiol during the follicular phase. Diet had no effect on non-esterified fatty acid or insulin concentrations, or on the duration of the oestrous cycle. The plasma concentration of 13,14,dihydro-15 keto PGF2α after administration of 50 iu oxytocin was unaffected by diet on day 15 and day 16 of the oestrous cycle, but showed a greater response on day 17 in the LA (n-6) supplemented group. Therefore, the PUFA content of the diet can influence both ovarian and uterine function in cows. However, further studies using larger numbers of cows are required to test whether fertility is also affected by such diets.

Rearing quality dairy heifers is essential to maintain herds by replacing culled cows. Information on the key factors influencing the cost of rearing under different management systems is, however, limited and many farmers are unaware of their true costs. This study determined the cost of rearing heifers from birth to first calving in Great Britain including the cost of mortality, investigated the main factors influencing these costs across differing farming systems and estimated how long it took heifers to repay the cost of rearing on individual farms. Primary data on heifer management from birth to calving was collected through a survey of 101 dairy farms during 2013. Univariate followed by multivariable linear regression was used to analyse the influence of farm factors and key rearing events on costs. An Excel spreadsheet model was developed to determine the time it took for heifers to repay the rearing cost. The mean±SD ages at weaning, conception and calving were 62±13, 509±60 and 784±60 days. The mean total cost of rearing was £1819±387/heifer with a mean daily cost of £2.31±0.41. This included the opportunity cost of the heifer and the mean cost of mortality, which ranged from £103.49 to £146.19/surviving heifer. The multivariable model predicted an increase in mean cost of rearing of £2.87 for each extra day of age at first calving and a decrease in mean cost of £6.06 for each percentile increase in time spent at grass. The model also predicted a decrease in the mean cost of rearing in autumn and spring calving herds of £273.20 and £288.56, respectively, compared with that in all-year-round calving herds. Farms with herd sizes⩾100 had lower mean costs of between £301.75 and £407.83 compared with farms with <100 milking cows. The mean gross margin per heifer was £441.66±304.56 (range £367.63 to £1120.08), with 11 farms experiencing negative gross margins. Most farms repaid the cost of heifer rearing in the first two lactations (range 1 to 6 lactations) with a mean time from first calving until breaking even of 530±293 days. The results of the economic analysis suggest that management decisions on key reproduction events and grazing policy significantly influence the cost of rearing and the time it takes for heifers to start making a profit for the farm.