Low doses of bovine somatotropin enhance conceptus development and fertility in lactating dairy cows.

Objectives were to evaluate the effects of administering either one or two low doses of slow-release recombinant bovine somatotropin (bST) on hormone concentrations, conceptus development, and fertility in dairy cows. Cows from two farms were detected in estrus on or after 50 days postpartum (n = 1483), inseminated, and enrolled in the study (Day 0). Within farm, cows were blocked by parity and assigned randomly to receive a single placebo injection at insemination (control), a single injection with 325 mg of bST at insemination (S-bST), or two injections with 325 mg of bST administered on Days 0 and 14 (T-bST). From a subset of cows, blood was collected twice weekly from Day 0 to 42 for determination of hormone concentrations and on Day 19 for isolation of leucocytes and analysis of transcript abundance of selected interferon-stimulated genes. Pregnancy was diagnosed on Days 31 and 66, and ultrasonographic morphometry of the conceptus was performed on Days 34 and 48 in a subset of cows. Cows that received T-bST had increased plasma concentrations of GH and IGF1 for 4 wk, increased mRNA expression of ISG15 and RTP4 in leukocytes, earlier rise in the pregnancy-specific protein B in plasma of pregnant cows, increased conceptus size, and enhanced fertility. Cows that received S-bST had increased concentrations of GH and IGF1 for only 2 wk and it was insufficient to alter conceptus development and fertility. In conclusion, supplementation with low doses of bST during the pre- and peri-implantation periods enhanced conceptus development, reduced embryonic losses, and improved fertility in dairy cows.

Effects of fertility on gene expression and function of the bovine endometrium.

Infertility and subfertility are important and pervasive reproductive problems in both domestic animals and humans. The majority of embryonic loss occurs during the first three weeks of pregnancy in cattle and women due, in part, to inadequate endometrial receptivity for support of embryo implantation. To identify heifers of contrasting fertility, serial rounds of artificial insemination (AI) were conducted in 201 synchronized crossbred beef heifers. The heifers were then fertility classified based on number of pregnancies detected on day 35 in four AI opportunities. Heifers, classified as having high fertility, subfertility or infertility, were selected for further study. The fertility-classified heifers were superovulated and flushed, and the recovered embryos were graded and then transferred to synchronized recipients. Quantity of embryos recovered per flush, embryo quality, and subsequent recipient pregnancy rates did not differ by fertility classification. Two in vivo-produced bovine embryos (stage 4 or 5, grade 1 or 2) were then transferred into each heifer on day 7 post-estrus. Pregnancy rates were greater in high fertility than lower fertility heifers when heifers were used as embryo recipients. The reproductive tracts of the classified heifers were obtained on day 14 of the estrous cycle. No obvious morphological differences in reproductive tract structures and histology of the uterus were observed in the heifers. Microarray analysis revealed differences in the endometrial transcriptome based on fertility classification. A genome-wide association study, based on SNP genotyping, detected 7 moderate associations with fertility across 6 different chromosomes. Collectively, these studies support the idea that innate differences in uterine function underlie fertility and early pregnancy loss in ruminants. Cattle with defined early pregnancy success or loss is useful to elucidate the complex biological and genetic mechanisms governing endometrial receptivity and uterine competency for pregnancy.

Ovarian responses and embryo survival in recipient lactating Holstein cows treated with equine chorionic gonadotropin.

The objectives of Experiment 1 were to determine a dose of eCG that would increase total luteal volume and plasma progesterone (P4) concentration on estrous cycle Day 7 in cows. The objectives of Experiment 2 were to determine the effects of treating embryo recipient lactating Holstein cows with eCG on pregnancy per embryo transfer (P/ET). In Experiment 1, lactating dairy cows at 63 ± 3 d postpartum (DIM) received no treatment (control, n = 10), or 600 (eCG6, n = 19), or 800 (eCG8, n = 19) IU of eCG 2 d after the start of the ovulation-synchronization protocol, Day -8 (Day -10 GnRH, Day -3 PGF(2α), Day 0 GnRH). Blood was sampled on Days -10, -8, -3, 0, 7, and 14 for P4 concentration. Ovaries were examined by ultrasound on Days -10, -3, 0, and 7. In Experiment 2, lactating dairy cows were paired according to parity and previous insemination (0 or > 1 insemination) and assigned to receive 800 IU of eCG (eCG8, n = 152) 2 d after the start of the ovulation-synchronization protocol (Day -10 GnRH, Day -3 PGF(2α), Day 0 GnRH) or to receive no treatment (control, n = 162). Blood was sampled on Days -10, -3, 0, 7, and 14 for determination of P4 concentration. Ovaries were examined by ultrasound on Days -10, -3, and 7, and cows with a CL > 20 mm in diameter on Day 7 received an embryo. In Experiment 1, P4 concentration on Day 7 was higher (P < 0.05) for eCG8 cows (2.3 ± 0.3 ng/mL) compared with control (1.2 ± 0.3 ng/mL) and eCG6 (1.1 ± 0.3 ng/mL) cows. In Experiment 2, eCG8 primiparous cows had more (P < 0.01) follicles > 10 mm on Day -3 compared with control primiparous cows (2.5 ± 0.9 vs 1.7 ± 0.5 mm), but multiparous control and eCG8 cows did not differ. A larger (P = 0.03) percentage of control cows received an embryo (87.5 vs 79.1%) compared with eCG8 cows. Among cows that received an embryo, total luteal volume on Day 7 was affected (P = 0.05) by treatment (eCG8 = 8.3 ± 0.4 cm(3), control = 6.2 ± 0.4 cm(3)), but P4 concentration on Day 7 did not differ significantly between treatments. The percentage of cows pregnant 53 d after ET (overall, 24.2%) was not significantly different between control and eCG8 cows. In the current study, no differences in P/ET were observed between control and eCG8 cows and treatment with eCG increased the percentage of cows with asynchronous estrous cycle.

Differential levels of mRNA transcripts encoding immunologic mediators in mammary gland secretions from dairy cows with subclinical environmental Streptococci infections.

Dry-off, and the period around parturition, are associated with increased susceptibility to intramammary infections in dairy cows. The immunological profiles of mammary gland secretions during these periods are not well described. The objective of the present study was to better characterize association(s) between chronic subclinical Environmental Streptococci infections at dry-off and relative levels of mRNA transcripts encoding multiple immunologic mediators present in cells derived from mammary gland secretions at dry-off and continuing through parturition. The chronic subclinical bacterial infections in the present study were characterized by multiple isolations of Streptococcus species and elevated SSC for a minimum of three weeks prior to dry-off. The majority of differences between principal and control quarters were identified at dry-off. Transcript levels of IL-17, IL2Rα and iNOS were increased while pro-inflammatory cytokine IL-6, and the regulatory cytokine IL-10, were reduced. Following antibiotic treatment of mammary glands, IL-17 transcripts remained elevated over the course of the study, indicative of a persistent insult. IL-4 transcript levels were modestly elevated at 7 days following dry-off and significantly elevated at 14 days, consistent with activated T(H)1 and T(H)2 lymphocytes in the principal quarters, respectively. From a temporal perspective, transcript levels of IL-8 decreased in all animals through the dry-off period animals and returned to pre-dry-off levels at parturition; levels of iNOS peaked at parturition. Five of the six principal cows experienced recurrent bacterial mastitis during the subsequent lactation; four were in the same quarter as was initially infected with Streptococcus and three of these four were due to coliforms. Taken together, this apparent chronic susceptibility of select mammary glands to bacterial infection would suggest a physiologic and/or immunologic dysfunction. Identification of factor(s) that contribute to the predisposition of mammary glands to developing mastitis should facilitate development of new control strategies.