Nonpuberal estrus in beef heifers

A note on attainment of puberty of september-born early-maturing ewe lambs in relation to level of nutrition

The attainment of puberty in September-born early-maturing ewe lambs was studied at Zaragoza (latitude 41° 40' N). Thirty twin Salz females were allocated to two groups receiving two nutrition levels after 3 months of age: high (500 g/day lucerne hay and 500 g/day concentrate) (H) and low (500 g/ day lucerne hay) (L). Oestrus was detected daily by aproned rams. Corpora lutea were counted after oestrus and plasma progesterone levels monitored each week.

In the first breeding season (January to February) the percentage of females showing sexual activity (silent emulation or oestrus and ovulation) was higher in the H compared with the L group (67 and 20%; P < 0/05). Nonpubertal oestrus before the main breeding season was detected in 67% of animals. In the main breeding season and for H and L groups respectively, percentage of females showing silent ovulation before puberty was 67 and 33% and mean age at puberty extended to 319 (s.e. 4-8) and 314 (s.e. 3·7) days. Ovulation rate at puberty was 1·73 (s.e. 0·13) and 1·33 (s.e. 0·15) respectively (P < 0·05).

Effect of the timing of controlled internal drug-releasing device insertion on the gonadotropin-releasing hormone-induced luteinizing hormone surge and ovulatory response

Concentrations of progesterone have been reported to influence GnRH-induced LH surges. At the beginning of many synchronization protocols, GnRH is used to synchronize follicular growth. Therefore, the objective of this study was to determine the effect of elevated concentrations of progesterone from a controlled internal drug-releasing device (CIDR) on the GnRH-induced LH surge and ovulatory response. Angus-cross beef heifers (n = 113; 41 pubertal and 72 prepubertal) were assigned to 1 of 3 treatments: 1) GnRH at CIDR insertion (CIDR-0), 2) GnRH 6 h before CIDR insertion (CIDR-6), or 3) GnRH 48 h after CIDR insertion (CIDR+48). Follicle size was determined before GnRH administration, and ovulatory response was determined 2 d later. Blood samples were collected from a subset of 60 heifers at -30, 0 (GnRH administration), 30, 60, 90, 120, 150, 180, 210, 240, 300, and 360 min after GnRH. Heifers receiving CIDR+48 had greater (P < 0.01) concentrations of progesterone compared with those receiving CIDR-0 and CIDR-6. There was no difference (P > 0.76) between treatments in concentrations of estradiol. There tended to be a cycling status x ovulation interaction on concentrations of progesterone (P = 0.11), and there was a cycling status x ovulation interaction on concentrations of estradiol (P = 0.02). The estradiol-to-progesterone ratio was significant because of treatment (P = 0.002), cycling status (P = 0.001), and a treatment x cycling status interaction (P = 0.02). Cycling status tended (P = 0.11) to have an influence on ovulation (29/41 and 42/72 for pubertal and prepubertal heifers). Ovulation was induced in more (P < 0.05) CIDR-0 (26/38) and CIDR-6 (28/37) heifers than CIDR+48 (17/38) heifers. There was no influence of treatment (P = 0.19), concentrations of estradiol (P = 0.90), or the estradiol-to-progesterone ratio (P = 0.21) on concentrations of LH, but there was an effect (P < 0.01) of progesterone on LH concentrations. Heifers with elevated progesterone at GnRH administration had a reduced LH surge compared with heifers with decreased concentrations of progesterone. Heifers that ovulated tended to have a greater (P = 0.11) magnitude of LH surge than heifers that did not ovulate. In summary, elevated concentrations of progesterone at GnRH administration decreased the GnRH-induced LH surge, and heifers in the CIDR+48 treatment had a decreased ovulatory response. However, there tended to be a difference in the magnitude of the LH surge only between heifers that did and did not ovulate.

Efeito da somatotrofina bovina (bST-r), do implante de progestágeno e do desmame por 72 horas na indução do estro e na taxa de prenhez em vacas

Este trabalho teve por objetivo avaliar a eficiência de tratamentos hormonais sobre a fertilidade de vacas de corte no pós-parto com diferentes condições corporais, durante a estação de monta de outono. Setenta e três vacas pluríparas cruzadas (Hereford x Nelore) criadas extensivamente, com condição corporal entre 2 e 4, foram pesadas e distribuídas em três grupos experimentais. O grupo GSED, constituído por 25 vacas, recebeu pessário vaginal (dia 0) contendo 250mg de acetato de medroxiprogesterona e 500mg de somatotropina bovina recombinante (bST-r). Na retirada dos pessários (dia 7), as vacas receberam 0,5mg de cipionato de estradiol e procedeu-se o desmame temporário dos bezerros por 72 horas. No grupo SED, 25 vacas receberam tratamento semelhante ao grupo GSED, porém não receberam bST-r. No grupo-controle, as 23 vacas somente foram separadas dos seus bezerros por 72h. Quando da retirada dos pessários as vacas foram colocadas com touros por 30 dias. Os animais foram pesados e avaliados quanto à condição corporal no início do experimento e na retirada dos touros (dia 37). Foi constatada perda média de peso de 0,648 kg/dia e os percentuais de estro foram de 26,1%, 33,3% e 56,5%, respectivamente, para os grupos controle, SED e GSED. O diagnóstico de gestação, realizado pela palpação retal 60 dias após a retirada dos touros, indicou percentuais de prenhez de 13,0%, 8,3% e 21,7%, respectivamente, para os grupos controle, SED e GSED (P=0,16), demonstrando que os programas hormonais adotados não foram eficientes no incremento das taxas de prenhez de vacas que perdiam peso entre 50 e 70 dias após o parto.

Some factors affecting the behavioural manifestation of oestrus in cattle: a review

The development of more efficient and cost-effective oestrous detection techniques for cattle depends on a thorough understanding of the changes in behaviour and physiology of the female during its oestrous cycle. Variability in the expression of oestrous behaviours both between individuals and over successive oestrous cycles complicates this process. This review considers many of the biological and environmental factors that influence the intensity and duration of oestrous behaviours in domestic cattle. Topics discussed include dominant-subordinate relationships, social facilitation, animal density, oestrous synchronisation, nutritional status, age and physiological state, presence of the bull and breed differences. Facility design, cattle management and various techniques used to detect oestrus (e.g. frequency, duration and timing of observations) directly influence the efficiency of oestrous detection programs. Environmental phenomena such as weather, day length, photoperiod and ambient temperature also affect the expression of oestrous behaviours.

Effect of acute nutritional restriction on incidence of anovulation and periovulatory estradiol and gonadotropin concentrations in beef heifers

The effects of acute nutritional restriction on follicular dynamics, incidence of anovulation, and periovulatory estradiol and gonadotropin concentrations were studied in two replicates using beef heifers exhibiting regular estrous cycles. Heifers fed a diet supplying 1.2 maintenance (1.2 Mn) were synchronized using an intravaginal progesterone-releasing device for 8 days. One day before device removal, heifers were allocated randomly, within replicate, to a diet supplying 0.4 Mn (n = 20), or kept at 1.2 Mn (n = 21). On the sixth day after detected ovulation, heifers received 500 microg of synthetic prostaglandin F(2alpha) (PGF(2alpha)) to induce luteolysis, estrus, and ovulation of the first dominant follicle (DF). Animals were inseminated and returned to a diet of 1. 2 Mn. Pregnancy diagnosis was performed 30 days later. The maximum diameter subsequently attained by the DF present at progesterone withdrawal was smaller (P < 0.01) in heifers fed 0.4 Mn. Two heifers fed 0.4 Mn failed to ovulate this DF (P > 0.10). Growth rate (P < 0. 01) and maximum diameter (P < 0.001) of the DF in the first follicular wave of the next estrous cycle was also reduced in heifers fed 0.4 Mn. After prostaglandin administration, a further 10 heifers fed 0.4 Mn failed to ovulate the first DF of this cycle, and it regressed (P < 0.001), causing anovulation in 12 of 20 heifers within 13-15 days (P < 0.001). Anovulation of the DF present at progesterone withdrawal was preceded by a proestrous estradiol increase but absence of a gonadotropin surge (2 of 2 heifers), while neither endocrine event was detected before anovulation of the DF of the first new follicular wave (2 of 2 heifers). In cases in which ovulation of the first DF of the new cycle occurred, fertility was similar (P > 0.10) in heifers fed either 0.4 (n = 7) or 1.2 Mn (n = 20). In conclusion, acute nutritional restriction of cyclic heifers from 1.2 to 0.4 Mn decreased the growth rate and maximum diameter of DFs and induced failure of the DF to ovulate in 60% of heifers, but, within the confines of limited animal numbers, did not compromise fertility in heifers that ovulated.

Endocrine and neural control of estrus in dairy cows

During proestrus, gonadotropins induce final follicular maturation, resulting in increased secretion of estradiol. Estradiol, in the relative absence of progesterone, acts on the hypothalamus to induce estrous behavior. The mean duration of estrus is 12 to 16 h and ranges from 3 to 28 h. The effects of estradiol appear to be "all or none". That is, once a threshold of estradiol is achieved, estrus is induced, and additional amounts of estradiol above threshold do not further enhance the estrous response (duration and intensity of estrus). Also, progesterone can block the estrus-inducing actions of estradiol. In addition, prior exposure to progesterone does not potentiate the estrus-inducing actions of estradiol except in the early postpartum period. In dairy cows, the first postpartum ovulation is often "silent". In other words, ovulation is not preceded by estrous behavior. High levels of estradiol during late gestation apparently induce a refractory state such that the brain cannot respond to the estrus-inducing actions of estradiol at the first postpartum ovulation. Progesterone can "reset" the brain, allowing it to respond to subsequent estradiol exposure. In the case of the postpartum cow, the corpus luteum formed after the first ovulation provides the progesterone that resets the brain. As a consequence, the second postpartum ovulation is preceded by estrous behavior. Finally, stress (or injection of ACTH) has been shown to delay, shorten, or inhibit completely the expression of estrus in the presence of estrus-inducing concentrations of estradiol.(ABSTRACT TRUNCATED AT 250 WORDS)

Estrous behavior and detection in cattle

Hormonal events determine the timing and maximum duration of estrous behavior, whereas environmental and social factors modulate or completely inhibit the expression of estrus. The efficiency of estrous detection can be improved on most livestock farms if more effort is given to visual observations of estrous behavior. Heat detection aids can be of value if used as a supplement to visual observations. Knowledge of factors that inhibit estrus can help producers avoid or minimize situations that make estrous detection difficult or impossible. Each livestock enterprise should have a customized heat detection program in place because blanket recommendations often fail when applied to many operations.

Female reproductive physiology and endocrinology of cattle

Maximizing reproductive efficiency is of major economic importance to dairy and beef producers. The development of new and improved methods of increasing reproductive performance depends on our understanding of the physiologic and endocrinologic mechanisms controlling the reproductive process. This article reviews the mechanisms associated with puberty, estrous cycles, pregnancy, parturition, and postpartum return to estrus.

Concentrations of 13, 14-dihydro-15-keto-prostaglandin F2α, estradiol-17β and progesterone during the peripubertal period in heifers

Twenty prepubertal Holstein heifers were utilized to assess plasma 13, 14-dihydro-15-keto-prostaglandin F(2)alpha (PGFM), serum progesterone (P(4)) and estradiol-17beta (E(2)) concentrations as well as the E(2):P(4) ratio during the onset of puberty in cattle. All animals were maintained as a group along with a sterile marker bull to assist in the detection of estrus. Upon detection of the first estrus (Day=O), daily blood samples were collected from a jugular vein until the heifers had completed 3 estrous cycles. The average body weight and age at first estrus were 247.6+/-4.8 kg and 304.0+/-7.5 days, respectively. Frequency of abnormal length estrous cycles was greater (P<0.02) during the first (40%) and second (35%) cycles than during the third estrous cycle (0%). All heifers had normal cycle lengths (18 to 24 days) by the third estrous cycle. Serum P(4) was greater during the third cycle (P<0.05) from Day 10 to Day 4 before the next estrus compared with the same period of the first estrous cycle. Serum E(2) did not peak until the day of estrus in the first cycle, whereas E(2) reached a maximal level 2 days before estrus in the third estrous cycle. Serum E(2) was higher (P<0.0001) 2 days before estrus in the third cycle than in the first estrous cycle. Plasma PGFM reached maximum concentrations 3 days before estrus in the third cycle compared with 1 day before estrus at the end of first estrous cycle. As estrus approached during the third cycle, PGFM rose 1 day before E(2) rose and P(4) declined, while the rise in PGFM and E(2) occurred simultaneously, with P(4) declining at the end of the first estrous cycle. During diestrus, the E(2):P(4) ratio was lower (P<0.07) in the third cycle than in the first, but it was higher (P<0.04) at estrus and 1 day before in the third estrous cycle. These data reveal a high incidence of abnormal length estrous cycles during the first two estrous cycles of the peripubertal period, and demonstrate anomalies in uterine and ovarian endocrine activity during the peripubertal period in cattle.

Plasma 13,14-dihydro-15-keto-prostaglandin F2 alpha concentrations in prepubertal dairy heifers challenged with oxytocin

Twenty-nine prepubertal Holstein heifers were assigned by age to one of three age groups to determine if the prepubertal bovine uterus could respond to an oxytocin stimulus. Group 1 heifers were 6 to 7 months of age (AGE1; n = 11), group 2 heifers were 8 to 9 months of age (AGE2; n = 11) and group 3 heifers were 10 to 11 months of age (AGE3; n = 7). Blood samples were collected via an indwelling jugular catheter. Four samples were collected at 15-min intervals prior to oxytocin administration to determine basal 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) concentrations. Each heifer received 100 IU of oxytocin i.v., blood sampling continued at 5 min intervals for the next 30 min and for an additional 90 min at 15-min intervals. Heifers were considered responders to oxytocin if mean PGFM concentrations increased at least 1.5 times the SD of their basal PGFM concentration. Age of the heifer (P less than .0001) and responder status (P less than .05) affected plasma PGFM. Plasma PGFM was higher in AGE1 and AGE3 heifers than AGE2 (P less than .0001). The number of responders was greatest at AGE3 (P less than .03) with AGE1 and AGE2 being similar. Mean basal PGFM was lower (P less than .04) at AGE2 than AGE1 with AGE3 being intermediate. In addition, basal PGFM at AGE1 tended to be lower (P less than .08) in the responders than in the non-responders, while AGE2 basal PGFM did not differ between responders and non-responders (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of dietary protein on age and weight at the onset of puberty in Brown Swiss and Zebu heifers in the tropics

The effects of dietary protein level on age and weight at onset of puberty were studied in the Mexican tropics using 12 Brown Swiss and 12 Zebu heifer calves in a completely randomized block design. The calves were weaned at 3 mo of age. They were confined in individual pens and fed either an adequate protein (12.8%) or a high protein (16.4%) diet ad libitum through the onset of puberty, which was defined as the first ovulation. To detect the first ovulation, heifers were palpated at 8 mo of age and then every 2 wk. At the detection of a developing follicle or any behavioral sign of estrus, they were palpated daily. Ovulation was confirmed by palpation of a corpus luteum. A blood sample for the determination of plasma progesterone concentration was taken with each palpation. There was a significant effect of breed on age at the onset of puberty, which was 9.4 and 12.3 mo for the Brown Swiss and Zebu heifers, respectively. Weight at puberty was 233 kg, independent of breed. Dietary protein had no effect on the onset of puberty. Brown Swiss heifers reach puberty earlier than Zebu heifers. Heifers in the tropics fed according to NRC recommendations reach puberty at ages comparable to those in temperate climate. This suggests that, if managed properly, calving age for Brown Swiss and Zebu heifers can be 24 and 27 mo, respectively. This is a considerable improvement from 36 to 48 mo of age now common in the area of study.