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This study evaluated the influence of feeding low and high preweaning allowances of unpasteurized whole milk (MA) on intake, selected blood metabolites, antibody response, mammary gland growth, and growth of New Zealand (NZ) dairy heifers to 7 mo of age. At 10 ± 2 d of age (study day 0), group-housed (six·pen−1) heifer calves (Holstein-Friesian × Jersey) were allocated to low (4 L whole milk·calf−1·d−1; n= 7 pens) or high (8 L whole milk·calf−1·d−1; n= 7 pens) MA for the next 63 d. Calves were gradually weaned between days 63 ± 2 and 73 ± 2. Calves in each pen had ad-libitum access to clean water, pelleted calf starter, and chopped grass hay from day 1 to 91 ± 2 d. At 92 ± 2 d, all calves were transferred to pasture, grazed in a mob, and their growth and selected blood metabolites were measured until day 209. All animals were weighed weekly during the indoor period (to day 91) and then at days 105, 112, 128, 162, 184, and 209. Skeletal growth measurements and blood samples to analyze selected metabolites were collected at the start of the experiment, weaning, and then postweaning on day 91, and day 201. Specific antibodies against Leptospiraand Clostridiawere quantified in weeks 7, 13, and 27. Mammary glands were scanned using ultrasonography at the start of the experiment, weaning, and day 201. Feeding high vs. low amounts of MA increased the preweaning growth in heifer calves (P =0.02) without negatively affecting postweaning average daily gain (ADG) (P= 0.74). Compared with heifers fed with low MA, high MA fed heifers had a greater increase in antibodies against Leptospiraand Clostridiaby 13 wk of age (P= 0.0007 and P= 0.06, respectively). By 27 wk of age, the antibody response was the same in heifers offered low or high MA. There was no effect of MA on the total size of the mammary gland, measured by ultrasonography, at weaning and 7 mo of age. However, the greater MA was associated with more mammary parenchyma (P= 0.01) and less mammary fat pad (P= 0.03) in back glands at 7 mo of age compared with heifers fed lower MA. In conclusion, feeding a high vs. a low amount of unpasteurized whole milk increased the preweaning growth of New Zealand replacement heifers without negatively affecting their ADG during postweaning under grazing conditions. Feeding more (8 vs. 4 L·d−1) unpasteurized whole milk positively affected antibody responses early in life and mammary gland composition by 7 mo of age in dairy heifers reared for pasture-based dairy systems.Greater milk feeding of calves resulted in greater growth rates to weaning, no negative effects on growth on pasture, at 13 wk of age had significantly greater serum-levels of antibodies against Leptospiraand Clostridia, and an increase in potential milk making tissue in their mammary glands at 7 mo of age.This study evaluated the effect of unpasteurized whole milk allowance on intake, antibody response, mammary gland growth, and growth performance of heifers until 7 mo of age. Feeding greater (8 L·d−1) vs. lower (4 L·d−1) milk allowance to heifer calves increased preweaning body weight without having any negative effect on postweaning growth under grazing. Heifers fed high milk allowance had significantly better antibody responses against Leptospiraand Clostridiaby 3 mo of age and had more mammary parenchyma (potential milk making tissue), and less mammary fat pad (supporting tissue) by 7 mo of age.

Modulation of the immune system is known to be important for successful pregnancy but how immune function might differ between the lymph nodes draining the reproductive tract and peripheral lymph nodes is not well understood. Additionally, if immune system changes in response to the presence of an embryo during early pregnancy, and if this response differs in local versus peripheral immune tissue, has not been well characterized. To address these questions, we examined expression of genes important for immune function using NanoString technology in the ampulla and isthmus of the oviduct, endometrium, lymph nodes draining the reproductive tract (lumbo-aortic and medial iliac) as well as a peripheral lymph node (axillary), the spleen, and circulating immune cells from ewes on day 5 of the estrous cycle or pregnancy. Concentrations of estradiol and progesterone in plasma were also determined. Principal component analysis revealed separation of the local from the peripheral lymph nodes (MANOVA P= 3.245e-08, R2= 0.3) as well as separation of tissues from pregnant and nonpregnant animals [lymph nodes (MANOVA P= 2.337e-09, R2= 0.5), reproductive tissues (MANOVA P= 2.417e-14, R2= 0.47)]. Nine genes were differentially (FDR< 0.10) expressed between lymph node types, with clear difference in expression of these genes between the lumbo-aortic and axillary lymph nodes. Expression of these genes in the medial iliac lymph node was not consistently different to either the axillary or the lumbo-aortic lymph node. Expression of IL10RBwas increased (FDR < 0.05) by 24% in the reproductive tissue of the pregnant animals compared to nonpregnant animals. Analysis of gene categories revealed that expression of genes of the T-cell receptor pathway in reproductive tract tissues was associated (P< 0.05) with pregnancy status. In conclusion, assessment of gene expression of reproductive and immune tissue provides evidence for a specialization of the local immune system around the reproductive tract potentially important for successful establishment of pregnancy. Additionally, differences in gene expression patterns in reproductive tissue from pregnant and nonpregnant animals could be discerned as early as day 5 of pregnancy. This was found to be associated with expression of genes important for T-cell function and thus highlights the important role of these cells in early pregnancy.