Use of Ultrasound in Reproductive Management of Beef Cow Herds

The use of ultrasound technology in reproductive management of beef cow herds is currently being evaluated in ongoing projects with cooperator herds in South Dakota. The projects include the use of ultrasound for the purposes of evaluating 1) cycling activity of heifers on estrous synchronization programs immediately prior to breeding and 2) early pregnancy detection and aging of fetuses in heifers and mature cows. Information obtained from these images will be used by producers to make management decisions associated with the breeding season, selection of heifers, and nutrition. Ovaries are evaluated for the presence of follicles and a corpus luteum, while pregnancies are determined from the presence or absence of a viable fetus. Age of the fetus is determined by the relative size of the fetus which can be measured by the machine. Initial data indicate that ultrasound technology can be used for all of the above mentioned purposes. One hundred fifty-eight heifers have been evaluated for cyclicity and 416 heifers have been scanned for early pregnancy. Pregnancy will be determined in 900 head of mature cows. As this is an ongoing project, calving data will be collected during the 1995 calving season to confirm ultrasound results

Endocrine Mechanisms of Puberty in Heifers: Estradiol Negative Feedback Regulation of Luteinizing Hormone Secretion

The hypothesis that luteinizing hormone (LH) secretion in prepubertal females is responsive to estradiol negative feedback and that decreased feedback occurs as puberty approaches was tested in heifers. In the first experiment, seven heifers were maintained prepubertal by dietary energy restriction until 508 days of age (Day 0). All heifers were placed on a high-energy diet on Day 0 at which time they received no additional treatment (CONT), were ovariectomized (OVX) or were ovariectomized and subcutaneously implanted with estradiol-17β (OVX-E2). This feeding regimen was used to synchronize reproductive state in all heifers. A second experiment was performed with 16 prepubertal heifers using the same treatments at 266 days (Day 0) of age (CONT, OVX and OVX-E2) but no dietary intake manipulation. In both experiments, LH secretion increased rapidly following ovariectomy in OVX heifers. In the initial experiment, LH secretion was maintained at a low level in OVX-E2 heifers until a synchronous rapid increase was noted coincidental with puberty in the CONT heifer. In the second experiment, LH secretion increased gradually in OVX-E2 heifers and attained castrate levels coincidental with puberty in CONT heifers. A gradual increase in LH secretion occurred as puberty approached in CONT heifers. These results indicate that: a) LH secretion in prepubertal heifers is responsive to estradiol negative feedback; and b) estradiol negative feedback decreases during the prepubertal period in beef heifers

Effects of Melengestrol Acetat (MGA) and Prostaglandin on Blood Serum Progesterone, Luteinizing Hormone, and Reproductive Performance in Beef Cows

A study utilizing 64 Angus and Simmental multiparous beef cows was conducted to evaluate the administration of MGA-PGF on the onset of estrus, conception rate, and to determine blood serum hormone profiles (P, & LH). Cows utilized were at least 30 days postpartum and stratified by age, breed, and days postpartum into two groups: a treatment group (n=32) which received MGA orally for 14 days and a control group (n = 32) which did not receive MGA. Cows in the study were bled weekly for 9 weeks to monitor serum P, levels. Cows with serum P4 ≥ 1 ng/mL were considered to have cyclic activity. Cows in both groups were injected with PGF2a 17 days after the last MGA feeding date and bred Al following observed estrus. The number of days from the start of MGA feeding to first detected estrus was lower for treated compared to control cows (19.50 a 3.70 and 34.31 a 3.28, respectively, P\u3c .01). The average number of julian days to first estrus was lower for treated compared to control cows (143.81 ± 2.46 and 154.34 ± 3.25, respectively, P= .01). Conception date in julian days was also lower for the treated animals compared to control cows (156.46 + 2.98 and 166.55 ± 3.21, respectively, P= .01). Treatment animals had a higher level of progesterone from the start of MGA feeding until the end of the bleeding period compared to the control animals (.41 ± .04 and .19 ± .04, respectively, P\u3c .001). The average progesterone hormone level in treated cows was higher 48 hours before injecting PGF,, compared to the control animals (1.59 ± .12 vs 0.33 ± .12, P\u3c .001). Blood serum analyzed for LH concentration was collected 3 days prior to PGF2a injection (Period 1) and 4 days following the PGF2a injection (Period 2). Mean LH levels between treatment and control groups were not different for the 7 days (1.58 ± .07 ng/mL and 1.70 ± .07 ng/mL, respectively, P= .25). When analyzed by periods, mean LH levels for Period 1 were lower (1.44 ± .08 ng/mL) than mean LH levels for Period 2 (1.84 a .07 ng/mL, P\u3c .01). Results from the present study suggest that MGA decreased days to first detected estrus, resulted in earlier conception, increased conception rate, increased progesterone hormone levels, and increased cyclic activity

Effect of Calving Time and Weaning Time on Cow and Calf Performance - A Preliminary Report

Cows grazing native range year round were allotted to 3 management systems: 1.) A calving season starting in mid March with calves weaned in late October; 2) A calving season starting in mid March with calves weaned in mid September; and 3) A calving season starting early May with calves weaned in late October. After 2 years of the study, pregnancy rate and calving interval were not affected by management system. Average weaning weight was the highest for the March calving/October weaned group in both years. In the first year of the study, severe winter weather caused a lower calf survival to weaning for the March calving groups compared to the May calving group. This resulted in similar pounds of calf weaned per cow exposed for the March calving/October weaned and May calving1October weaned groups. Estimated income per exposed female was similar for these two groups. In the second year of the study, calf death loss was not affected by calving time. The heavier weaning weights of the March calving /October weaned group resulted in more pounds weaned per cow exposed and $30 greater income per exposed female. The potential to reduce costs for winterfeed, equipment, calving facilities and labor would favor later calving and must be considered

Effects of MGA on Prepubertal Beef Heifers

A 2-year study (1 995 and 1996) utilized prepubertal beef heifers to study the effects of feeding MGA to induce puberty. Heifers were allotted to two groups, control or treatment, based on breed, age and weight. Treatment heifers received MGA for 14 days at a rate of .4 mglday with their diet, while control heifers received the same diet free of MGA. In year 1 (n = 55; control = 28, treatment = 27), heifers averaged 627.7 Ib and were 301.9 days of age at the start of the treatment. There was no difference in age at puberty (P=.65) with control heifers 378.5 rt8.3 days of age and treatment heifers 373.0rt8.5 days of age. Forty-seven of 55 heifers became pregnant during the breeding season (85.5%). Of the 47 heifers, 37 heifers gave birth to a live calf (78.7%). In year 2 (control =20, treatment = 21 ), heifers averaged 609.0 Ib and were 300.4 days of age at the start of the treatment. Control heifers were 373.6 ± 7.3 days of age and treatment heifers 382.4rt7.3 days of age at puberty (P= .40). Thirty-eight of 41 heifers became pregnant during the breeding season (92.7%). Thirty-five of 41 heifers were bred Al (85.4%). Thirteen of 16 control heifers and 12 of 19 treatment heifers became pregnant to Al (P\u3e.50). The use of MGA to induce puberty has potential, but further research is needed to determine the age at which it should be administered

Effects of MGA on Prepubertal Crossbred Beef Heifers

A study was conducted using 55 prepubertal replacement crossbred beef heifers to determine the effect of feeding MGA to prepubertal heifers on age at puberty. No difference (P= .65) was detected between MGA treated heifers versus control heifers for age at puberty. There was no difference (P= .80) in age at conception to A1 for the two groups

South Dakota Retained Ownership Demonstration

Three hundred seventy-four calves representing 44 cow-calf producers were consigned to a custom feedlot. Steer calves (254 head) consigned in October weighed 522 Ib initially, gained 2.91 1b per head daily, and averaged 1,100 Ib at slaughter after an average of 200 days on feed. Average cost of gain and profitability were $48.94 per cwt and -$12.03 per head, respectively. Steers consigned in January weighed 71 1 Ib initially, gained 3.07 Ib per head daily, and averaged 1,135 1b at slaughter after 141 days on feed. Average cost of gain and profitability were $43.59 per cwt and -$64.22 per head, respectively. Losses observed for 1994-95 were due to low carcass beef prices relative to the price of feeder cattle in fall of 1994 and January of 1995. As in previous years, average daily gain, days on feed, and quality grade appear related to differences in profit between cattle

South Dakota Retained Ownership Demonstration

Seven hundred six calves representing 81 cow-calf producers were consigned to a custom feedlot. Steer calves (421 head) consigned in October weighed 562 Ib initially, gained 2.75 Ib per head daily, and averaged 1153 1b at slaughter after an average of 207 days on feed. Average cost of gain and profitability were $61.48 per cwt and -$86.61 per head, respectively. Steers consigned in January weighed 738 Ib initially, gained 3.36 Ib per head daily, and averaged 1,196 Ib at slaughter after 137 days on feed. Average cost of gain and profitability were $55.55 per cwt and 4123.1 1 per head, respectively. Heifers consigned in January weighed 683 Ib initially, gained 3.17 Ib per head daily, and averaged 1063 1b at slaughter after 122 days on feed. Average cost of gain and profitability were$58.39 per cwt and -$95.63 per head, respectively. Severe losses observed for 1993-94 were due to a crash in the carcass beef market in late May through July as compared to the previous 3years of the Retained Ownership Demonstration. As in previous years, average daily gain, days on feed and percentage of choice appear to be related to differences in profit between cattle

Effects of 17β-Estradiol on Distribution of Pituitary Isoforms of Luteinizing Hormone and Follicle-Stimulating Hormone during the Follicular Phase of the Bovine Estrous Cycle

The objective of this study was to examine the influence of 17β-estradiol (E2) on distribution of LH and FSH isoforms during the follicular phase of the bovine estrous cycle prior to the preovulatory surges of LH and FSH. On Day 16 of the estrous cycle (Day 0 = estrus), intact controls (CONT; n = 4) were treated with prostaglandin F2α (PGF2α) to induce luteal regression and initiation of the follicular phase. Other cows were also treated with PGF2α and either ovariectomized (OVX; n = 5) or ovariectomized and given E2 implants (OVXE; n = 6) to mimic the pattern of increasing E2 concentrations during the follicular phase of the estrous cycle. Pituitaries were collected 40 h after treatment with PGF2α, or ovariectomy (0 h). Aliquots of pituitary extracts were chromatofocused on pH 10.5-4.0 gradients. The LH resolved into thirteen isoforms (designated A-L and S, beginning with the most basic form) while FSH resolved into nine isoforms (designated I-IX, beginning with the most basic form). The percentage of LH as isoform F (elution pH = 9.32 + 0.01) was greater (p \u3c 0.05) in the OVX group (48.5%) than in the OVXE group (45.0% ). LH isoforms I (elution pH = 6.98 ± 0.01) and J (elution pH = 6.48 ± 0.01) were more abundant (p \u3c 0.05) in cows from the OVXE (2.3 and 5.8%, respectively) than the OVX group (1.4 and 3.7%, respectively). Distribution of LH isoforms in cows from the three groups did not differ (p \u3e 0.10). Distribution of FSH isoforms were similar (p \u3e 0.05) among all groups. In summary, removal of the ovary (OVX) resulted in a slight increase in percentage of the basic LH isoform F, while removal of the ovary and administration of E2 (OVXE) in a pattern that mimicked increasing concentrations of E2 during the follicular phase of the estrous cycle resulted in a slight increase in the percentage of acidic LH isoforms (I and J). There was no influence of ovariectomy or treatment with E2 on distribution of FSH isoforms in the pituitary. Thus, gonadotropin heterogeneity does not appear to change significantly during the follicular phase of the bovine estrous cycle

Structural subnetwork evolution across the life-span: rich-club, feeder, seeder

The impact of developmental and aging processes on brain connectivity and the connectome has been widely studied. Network theoretical measures and certain topological principles are computed from the entire brain, however there is a need to separate and understand the underlying subnetworks which contribute towards these observed holistic connectomic alterations. One organizational principle is the rich-club - a core subnetwork of brain regions that are strongly connected, forming a high-cost, high-capacity backbone that is critical for effective communication in the network. Investigations primarily focus on its alterations with disease and age. Here, we present a systematic analysis of not only the rich-club, but also other subnetworks derived from this backbone - namely feeder and seeder subnetworks. Our analysis is applied to structural connectomes in a normal cohort from a large, publicly available lifespan study. We demonstrate changes in rich-club membership with age alongside a shift in importance from 'peripheral' seeder to feeder subnetworks. Our results show a refinement within the rich-club structure (increase in transitivity and betweenness centrality), as well as increased efficiency in the feeder subnetwork and decreased measures of network integration and segregation in the seeder subnetwork. These results demonstrate the different developmental patterns when analyzing the connectome stratified according to its rich-club and the potential of utilizing this subnetwork analysis to reveal the evolution of brain architectural alterations across the life-span