Effect of gonadotropin-releasing hormone at estrus on subsequent luteal function and fertility in lactating Holsteins during heat stress.

The experiment used lactating Holstein cows (n = 94) from three herds in Mississippi. The experiment was conducted during late summer when temperatures were hot enough to cause a measurable stress response in cows in order to determine the effect of GnRH administration during estrus on fertility and subsequent luteal function of cows under these conditions. The mean ranges for ambient temperature, relative humidity, and temperature-humidity index during the study were 21.4 to 32.8 degrees C, 67 to 95%, and 21.6 to 29.6, respectively. After injection of PGF2 alpha for synchronization of estrus, cows were alternately injected with 100 micrograms of either GnRH or saline (control) at detection of estrus, followed by AI 10 to 12 h later. From 14 treated cows and 14 control cows, blood samples were drawn by venipuncture just prior to treatment and at 5-d intervals until 30 d after treatment. Serum progesterone concentrations were determined by radioimmunoassay. Mean progesterone concentrations were higher for the cows treated with GnRH than for the controls. The pregnancy rate from first AI was 28.6% for all treated cows and 17.7% for control cows. On d 20, 42.8% of the treated cows and 57.1% of the control cows exhibited progesterone concentrations that were typical of pregnancy. When pregnancy was diagnosed in these cows after d 45, pregnancy rates had decreased significantly for controls but not for cows given GnRH at estrus, suggesting greater embryonic survival in treated cows. We concluded that GnRH treatment enhanced secretion of luteal progesterone and embryo survival.

Corpus luteum growth and function in lactating Holstein cows during spring and summer.

Corpus luteum growth and function were monitored daily for a complete estrous cycle by ultrasonography and peripheral serum progesterone in lactating, cyclic Holstein cows during spring (n = 8) and summer (n = 8). For spring and summer, respectively, daily ambient temperatures (mean +/- SEM) were 21.2 +/- .9 and 31.1 +/- .3 degrees C. In summer compared with spring, early morning rectal temperatures were higher on d 1, 2, and 3, when the corpus luteum was forming, and on d 15 and 19. The length of the luteal phase and the corpus luteum cross-sectional area were similar for the two seasonal groups. Central luteal cavities were observed during spring and summer. Serum progesterone secreted between d 6 and 18 was lower during summer. In addition, progesterone concentrations during the entire luteal phase and the peak magnitude of progesterone tended to be lower during summer. Suppressed luteal function may contribute to low fertility when cows are inseminated during summer.

Estrous and endocrine responses of lactating Holsteins to forced ventilation during summer.

Fourteen lactating and cycling Holsteins in each of two summers were assigned randomly to pens in a free-stall barn either with or without overhead fans to study the effect of fan cooling on certain endocrine and behavioral responses during the estrous cycle. After an adjustment period of 8 d in the first summer and 21 d in the second summer, jugular cannulas were inserted, and 25 mg of PGF2 alpha were injected. After injection, blood samples were collected frequently for 84 h in the first summer and 88 h in the second summer, followed by collection three times weekly for 3 wk thereafter each summer. Rectal temperatures were lower in the group cooled by fans than in the control group each summer. Luteal progesterone secretion tended to be greater in the fan group each summer; area under the luteal phase curve was significantly higher than for controls during the second summer. There was tendency for more preovulatory surges of LH and higher estrous responses rates in the fan group during the second summer. Thus, fan cooling of lactating dairy cows for several weeks before anticipated breeding provides potential for more efficient reproductive performance during the summer.

Estrous cyclicity in nonlactating and lactating Holsteins and Jerseys during a Pakistani summer.

Data from 36 cows were used in a 2 x 2 factorial arrangement to determine the effects of breed and lactation status on estrous cyclicity during a Pakistani summer (June through October). Cows were selected from a herd of Holsteins and Jerseys imported from the United States 5 yr earlier. Ambient temperatures were highest in June and declined in the ensuing months with the onset of the rainy season. Relative humidity increased in July and August and them remained stable until the end of the study. Although early morning rectal temperatures gradually declined from June through October, late afternoon rectal temperatures were highest in August. Average early morning rectal temperatures were higher in Holsteins than in Jerseys (38.5 vs. 38.3 degrees C). Even though all cows were cyclic throughout the study, as indicated by patterns of progesterone secretion, observed expression of estrus was low (36.8%) and unaffected by breed or lactation status. Average serum progesterone concentrations were lower (2.4 vs. 3.1 ng/ml), and cortisol concentrations were higher (4.1 vs. 3.9 ng/ml), in Holsteins than in Jerseys. Breed by lactation status interactions were significant for lengths of the luteal phase and estrous cycle. Lengths for lactating Holsteins were longer than those of other groups.

Effects of late gestation heat stress on postpartum milk production and reproduction in dairy cattle.

Carry-over effects of late gestation heat stress on postpartum productive and reproductive traits were estimated from DHI records using 341 lactations from six sites in Mississippi. Climatological data were gathered from records of weather stations near the sites. Using multiple linear regression analyses, predictor variables for lactations were age at calving, lactation number, maximum degree-days (above 32.2 degrees C) during the periods 30 and 60 d prepartum, and precipitation 30 and 60 d prepartum. Months and sites were indicator variables. Dependent variables included milk and fat production during early, mid, and late lactation; days to peak lactation; days open; services per conception; and body weight. Age at calving affected milk and fat production in mid and late lactation and services per conception. Degree-days for 60 d prepartum had the greatest negative influence on production variables; its statistical significance was shown in predictions of milk and fat production in early and midlactation. Days open were higher for July than for cows calving in August or September. Sites had effects on many milk and fat measurements and some reproductive traits. These results indicate that heat stress in the last 60 d of gestation has negative effects on some production variables.

Synchronization of estrus in early diestral dairy heifers with Prostaglandin F(2)alpha and estradiol benzoate.

Following observation of estrus, 134 Holstein heifers were given injections of Prostaglandin F(2)alpha (PGF(2)alpha) between Days 5 and 10 of their cycle (estrus = Day 0). They were then randomly assigned to either a group receiving 400 microg of estradiol benzoate (E(2)B) 40 h or maintained as controls. Heifers observed in estrus within 120 h of PGF(2)alpha administration were inseminated (approximately 12 h after initial observation of estrus). Blood samples for progesterone determination were drawn from the coccygeal vein on Days 15 and 21 after insemination. Pregnancy was confirmed by palpation per rectum between Days 5.0 and 60 post insemination. When control and treated heifers were compared it was found that a higher percentage of heifers treated with E(2)B exhibited estrus after PGF(2)alpha, but there had been no effect on subsequent progesterone concentrations or pregnancy rates.

Patterns of oviducal motility in the cow during the oestrous cycle.

Microtransducers sensitive to changes in internal diameter were chronically implanted in the oviducts of 5 dairy cows. Motility patterns were recorded throughout 9 oestrous cycles. Cyclic variations in patterns of motility were observed and compared with circulating concentrations of plasma progesterone. Luteal-phase motility patterns were of low amplitude and frequency. The frequency and amplitude of motility increased 3-5 days before behavioural oestrus. This activity consisted primarily of longitudinal muscle contractions, with an interspacing of circular muscle activity occurring during oestrus. Patterns of activity after oestrus were similar to those before oestrus, with activity decreasing 3-5 days after oestrus. Transducers implanted bilaterally in 2 animals permitted observation of asynchronous patterns between right and left oviducts. Preliminary data suggested a higher level of activity in the oviduct ipsilateral to the active ovary. These variations may be due to a local effect, possibly mediated by the functional ovary or the ovum.

Response of dairy heifers to Prostaglandin F2alpha after treatment with human chorionic gonadotropin.

After the observation of estrus following administration of Prostaglandin F2alpha (PGF2alpha), 79 dairy heifers were randomly either injected with 2500 IU of human chorionic gonadotropin (hCG) 48 h postestrus or maintained as controls with no injection at that time. Five to 9 d later, after a blood sample for progesterone determination was taken, all heifers were injected with 25 mg of PGF2alpha. Heifers observed in estrus within the next 5 d were inseminated about 12 h after initial observation and were palpated for pregnancy 45 to 60 d postinsemination. Heifers treated with hCG had higher progesterone concentrations, reduced and delayed estrual responses, and lower insemination fertility rates when compared with control heifers.

Insemination management for a one-injection prostaglandin F(2)alpha synchronization regimen. I. One daily insemination period versus use of the a.m./p.m. rule.

Following detection of estrus in a one-injection prostaglandin F(2)alpha (PGF(2)alpha) synchronization regimen, 261 dairy heifers were randomly inseminated (A.I.) either once between 0800 and 0900 h daily (a.m.) or about 12 h after detection of estrus (a.m./p.m.). During the regimen, 31.8 and 33.3% for the a.m./p.m. and a.m. groups, respectively showed estrus and received A.I. during the pre-PGF(2)alpha period. The remaining heifers were injected with PGF(2)alpha with 95.6% from a.m./p.m. and 96.5% from a.m. showing estrus and receiving A.I. within five days after PGF(2)alpha. Pregnancy rates of 62.9% for a.m./p.m. and 62.0% for a.m. did not differ. Progesterone at the time of injection was similar between groups and was not correlated with either response to PGF(2)alpha or fertility. Percentages of heifers in estrus <24, 25-48, 49-72, 73-96 and >96 after PGF(2)alpha were 4.7, 30.2, 45.6, 14.3 and 5.3, respectively, with a mean time of 61.0+/-1.9 h. Satisfactory conception rate was attained with a.m. insemination.

Insemination management for a one-injection prostaglandin F(2)alpha synchronization system. II. One versus two inseminations following detection of estrus.

Following detection of estrus in an estrus synchronization system, 216 dairy heifers were inseminated (A.I.) randomly either soon after detected estrus (1X) or soon after detected estrus and again 10 to 12 h later (2X). Average h from detection of estrus to A.I. was 1.8+/-0 for 1X and 1.1+/-0 and 11.1+/-0.4 for 2X. During the regimen, heifers were checked visually for estrus daily for five consecutive days with 16.0 and 17.3% showing estrus and receiving A.I. in the 1X and 2X groups, respectively. Those not seen in estrus were injected with 25 mg PGF(2)alpha with observations for estrus and A.I. continuing for five more days. Response rates as indicated by estrus following prostaglandin F(2)alpha (PGF(2)alpha) were 74.7 and 75.8% for 1X and 2X, respectively. Percentages of heifers in estrus <24, 25 to 48, 49 to 72, 73 to 96 and >96 h after PGF(2)alpha were 3.7, 22.8, 47.1, 15.4 and 11.0, respectively. Based on rectal palpation for pregnancy between 45 and 60 days after A.I., conception rates of 70.2% for 1X and 68.6% for 2X did not differ significantly (P>0.05). Progesterone concentrations at injection for heifers not responding to PGF(2)alpha were lower than was seen in responding heifers (2.7 vs 5.8 ng/ml) (P<0.01). Data from the present experiment supports the conclusion of an earlier experiment that satisfactory conception can be achieved with a single, established daily insemination period.

Response and fertility of dairy heifers following injection with prostaglandin F(2alpha) during early, middle or late diestrus.

After an observed estrus, 250 dairy heifers were injected once with 25 mg of PGF(2alpha) either on cycle days 5 through 7 (E), 8 through 11 (M) or 12 through 15 (L). For five days after the PGF(2alpha) injection, heifers were inseminated at about 12 h after estrus was first observed. Observed estrual response rates were 43.0%, 83.6% and 100% for E, M and L, respectively. Average time from PGF(2alpha) to observation of estrus for E, M and L was 59, 70 and 72 h. Conception rates for heifers responding to PGF(2alpha) were 56.8%, 62.1% and 78.3% for E, M and L, respectively. Based on blood samples drawn at the time of PGF(2alpha) injection, progesterone concentration was significantly correlated with response rate but not with conception rate. When compared with M and L, E had a significantly lower response rate and conception rate as well as a shorter period between injection of PGF(2alpha) and observation of estrus.

Influence of the pituitary-adrenal axis on the induced release of luteinizing hormone in rams.

Treatment of intact rams with ACTH increased plasma corticosteroids and significantly reduced the ability of LH releasing hormone (LHRH) to elicit the release of LH. Infusion of cortisol at a rate which increased plasma corticosteroid concentrations to above that observed after injection of ACTH did not affect the ability of LHRH to induce the release of LH. In adrenalectomized rams LH release in response to LHRH was inhibited during ACTH treatment but was not affected in the absence of ACTH. Therefore, ACTH reduced the responsiveness of the anterior pituitary gland to LHRH through a mechanism not involving the adrenal gland.

Heat stress as it affects animal production.

It is well documented that the stress of hot environments lowers productive and reproductive efficiency, in farm animals. Likewise, research information is available to aid in the management of livestock in such adverse conditions. However, practical methods to achieve the desired levels of productive and reproductive performance are lacking. Summer forages that will support a high level of productivity in subtropic and tropic regions are needed for ruminants. More critical information is needed on the total dietary needs of all farm animals in hot environments. Dietary emphasis should be to increase intake or to alter levels of proteins, amino acids or other nutrients to improve the conversion of feed units into production units. Increasing nutrient intake to support a higher level of production will render animals more sensitive, in terms of productive efficiency, to environmental modifications that improve comfort. This should be especially pertinent in the humid Southeast and other regions where production responses to environmental modifications have been variable. There is limited information on the effect of the night cooling cycle on productive efficiency and on the effect of severe heat stress on reproductive phenomena not related to conception.

Routine postpartum treatment of dairy cattle with intrauterine neomycin sulfate boluses.

Within location, 119 dairy cattle from two experiment station herds, which had no problems associated with parturition, were randomly either treated by insertion of two intrauterine boluses containing a total of 1000 mg neomycin sulfate 24 h postpartum or maintained as a control. Uteri and ovaries of all cows were palpated 17 to 24 days postpartum and at 14 day intervals thereafter until inovulation of the uterus was judged complete and an estrus had been observed. All cows were inseminated at the first estrus after 60 days postpartum and at each estrus thereafter until conception. Cows treated with neomycin sulfate required more services per conception (1.7 to 1.4) and were open more days before conception (100.5 to 88.5) than the controls. The probable cause of the lowered reproductive efficiency is discussed. Treatment did not later significantly days to ovulation, estrus, involution, or first service. Three treated and five control animals needed additional uterine treatment. Routine intrauterine treatment of all cows with neomycin sulfate boluses should not be recommended.