Effect of an inverse subtropical (19 degrees 13'N) photoperiod on ovarian activity, melatonin and prolactin secretion in Pelibuey ewes

Reproductive seasonality of hair rams under tropical conditions: an alternative for non-seasonal lamb production?

Reproductive seasonality limits the periods of breeding on the year and, therefore, productive output. However, some breeds appear as probably non-seasonal. The aim of the study was to characterize the seasonal pattern of Santa Inês rams, including an ultrasound characterization of the reproductive tract, testosterone concentrations, and semen characteristics. Fifteen Santa Inês rams remained in a grazing system with concentrate supplementation, and measurements of the reproductive tract and ultrasound evaluation (biometrics and pixel intensity) of the testicles and accessory sex glands were monthly recorded. Computerized seminal evaluations were also performed monthly, and serum testosterone concentration was measured every 15 days. Body weight and condition remained stable throughout the year. In general, reproductive traits varied along the year and reached maximum values during autumn and minimum in spring. Despite that, as fresh semen remained with enough quality to breed all along the year, seasonality does not appear as a limiting factor to breed along the year. Therefore, Santa Inês rams can be used for all-year-round breeding or for crossbreeding when rams from other breeds decrease their fertilizing ability.

Lambing rate and prolificacy in inseminated hair sheep treated with bovine somatotropin

This study evaluated whether the administration of 50 and 100 mg bovine somatotropin (bST) at the start of estrous synchronization and at the time of artificial insemination improves lambing rate and prolificacy in hair sheep. Four hundred eighty adult hair ewes (Pelibuey, Blackbelly, Dorper, Katahdin, and their crosses) were synchronized with intravaginal sponge containing 40 mg of fluorogestone acetate. On the day of sponge insertion, ewes were assigned to three treatments: the bST-100 treatment (n = 156) received 100 mg bST at the start of synchronization (d 0) and at the time of insemination (d 14), the bST-50 treatment (n = 159) received 50 mg bST in the same schedule as the previous group, and the control (n = 165) did not receive any bST. Lambing rate and percentage of multiple births were analyzed using the GENMOD procedure of SAS. Prolificacy data were analyzed using the MIXED procedure of SAS. The IGF-1 and insulin concentrations were analyzed with ANOVA for repeated measures. The bST application did not affect the lambing rate (P = 0.06). The proportion of ewes with multiple births (P = 0.01) and prolificacy (P = 0.04) were higher in the bST-50 (54.3% and 1.57 ± 0.1) than the bST-100 (18.2% and 1.25 ± 0.1) and control (33.3% and 1.28 ± 0.1) groups. The IGF-1 and insulin concentrations were higher (P < 0.05) in the bST-treated groups, but the insulin concentration was higher (P = 0.001) in the bST-100 group than in the bST-50 group. The administration of 50 or 100 mg bST at the start of synchronization and at the time of artificial insemination does not increase lambing rate. However, the dose of 50 mg increased the proportion of multiple births and prolificacy.

Reproductive seasonality in creole hair sheep in the tropic

The objective of the present study was to evaluate the annual ovulatory activity of hair sheep at 15° N. Nineteen Creole ewes with body weight of 40.8 ± 0.3 kg were used. The ovulatory activity was monitored for a year by quantifying progesterone concentrations in blood samples obtained from all the ewes every 7 days. The differences in monthly proportions of ewes with ovulatory activity were analyzed by the chi-square test. Ovulatory activity decreased from May to July and in September, and 42% of ewes ovulated year round. It is concluded that at 15° N, a high proportion of ewes is capable of ovulating throughout the year in the tropical southeastern region of Mexico.

Influence of space allowance and housing conditions on the welfare, immune response and production performance of dairy ewes

The experiment used 45 Comisana ewes, divided into 3 groups of 15. The aim was to determine the effects of two different stocking densities and two different housing conditions on welfare, and on production performance of dairy ewes. The stocking densities tested were: high stocking density (1·5 m2/ewe, HD group) and low stocking density (3 m2/ewe, LD group); the two housing conditions tested were: ewes housed indoors (LD group, 3 m2/ewe) and ewes allowed to use an outdoor area (LDP group, 3 m2/ewe divided into 1·5 m2/ewe indoors and 1·5 m2/ewe outdoors). At the beginning of the experiment, and then every 2 months, the cell-mediated immune status of sheep was evaluated. One month after the beginning of the experiment, and 20 d later, the ewes were injected with chicken egg albumin (OVA) to assess their humoural immune responses. Starting from the beginning of the experiment and then monthly, behavioural activities of ewes were monitored using 15-min scans. After lamb weaning, milk yield from individual ewes was measured and milk composition analysed weekly. Housing conditions (low density reared ewes indoors v. low density reared ewes with free access to an outdoor area) affected cell-mediated response, which was higher in LDP than in LD ewes. Concentrations of anti-OVA IgG were mainly influenced by space allowance, with higher antibody titres in LD than in HD ewes throughout the experiment. Both housing conditions and space allowance affected sheep behavioural activities: a greater proportion of LDP ewes displayed standing and drinking behaviours than LD ewes, and a greater proportion of LD ewes was observed walking than HD ewes. Ewes allowed access to the outdoor area had a higher protein content and lower somatic cell count in their milk, whereas reduced space allowance led to a reduction in milk yield and an increase in somatic cell count of milk. Results indicate that both increased space allowance and availability of outdoor area can improve the welfare and production performance of the lactating ewe.

Reproductive activity of Pelibuey and Suffolk ewes at 19° north latitude

Under photoperiod regulated conditions, some Pelibuey ewes appear to express estrous cycles continuously throughout the year. Ovulatory activity of Suffolk ewes has not being determined at 19 degrees N. The aim of the present study was to describe the annual reproductive cycle of Pelibuey and Suffolk ewes under natural conditions at 19 degrees N. Ten adult ewes of each breed were maintained under natural environmental conditions, on a constant plane of nutrition and isolated from rams. The ovulatory activity of both breeds was monitored over 2 years (2003 and 2004) by quantifying progesterone concentrations in blood samples taken twice a week. For both breeds, the proportion of ovulating ewes per month and year was analyzed by chi(2). The duration of anestrus was compared between breeds and years by analysis of variance. Correlation of ambient temperature and weight changes with the ovulatory activity was evaluated by regression procedure. Ovulatory activity was different (P<0.05) between breeds from February to July. Pelibuey sheep (60%, 6 of 10) ovulated continuously during the entire study; one animal was eliminated in the second year, due to ovarian follicular cysts and three ewes had anestrous periods from 65+/-46 to 70+/-36 days. Suffolk ewes displayed reproductive seasonality similar to that observed in sheep of the same breed in latitudes greater than 35 degrees . Within breed, reproductive behavior of sheep was similar between years, with the only difference (P<0.05) observed in February for Pelibuey and in July for Suffolk relative to other months. Ambient temperature was not correlated with ovulatory activity. The body weight of Pelibuey ewes was constant during the entire study and was not correlated with ovulatory activity. There was, however, an increase on the body weight of Suffolk ewes, but this variation was not related to ovulatory activity. These findings lead to the conclusion that at 19 degrees N, a high proportion of Pelibuey ewes is capable of ovulating throughout the year, whereas Suffolk ewes undergo seasonal anestrous periods similar to those observed in individuals of the same breed at latitudes greater than 35 degrees . Identification of continuous ovulatory Pelibuey ewes may be the first step for developing a selection program against seasonality to increase lambing frequency.

Effect of semen collection frequency on seasonal variation in sexual behaviour, testosterone, testicular size and semen characteristics of tropical hair rams (Ovis aries)

The purpose of this study was to examine the effect of day length on seminal characteristics, testicular size, sexual behaviour and testosterone (T4) concentration in pelibuey rams subjected to different semen collection frequencies. eighteen intact males were assigned randomly to one of two semen collection frequencies: in the high rate (HR) treatment, two ejaculations per week were obtained from each ram; one ejaculation every two weeks was collected under the low rate (LR) treatment. All animals were housed individually in contiguous 5 m x 5 m wire mesh pens and evaluated over a 12-month period. At the beginning of the experiment rams were 20 months old and 40-50 kg in weight. All rams ejaculated and produced semen throughout the year. Semen volume, sperm per ejaculation, testicular circumference and testicular volume were significantly (p < 0.05) greater during short days in all rams, regardless of the semen collection frequency, with the exception of sperm concentration, for which no variation was found in hr individuals, and reaction time and T4 levels, for which no variation was found in IR males. Rams subjected to HR collection were more affected by the short-day photoperiod than rams collected twice per week, exhibiting greater reduction (p < 0.05) in time to achieve their first ejaculation and in sperm per ejaculation, as well as greater increases (p < 0.05) in T4 concentration than IR rams (14.65 +/- 1.22 vs 23.53 +/- 5.34 s, (3.37 +/- 0.17) x 10(9) vs (3.52 +/- 0.20) x10(9) sperm and 8.68 +/- 0.44 vs 6.85 +/- 0.74 ng/ml, respectively). It was concluded that: (a) the magnitude of the seasonal effects was not sufficient to prevent the rams being used for breeding throughout the year, and (b) seasonal variation within variables was affected differently between semen collection frequencies.

Annual pattern of plasma melatonin and progesterone concentrations in hair and wool ewe lambs kept under natural photoperiod at lower latitudes in the southern hemisphere

To study the annual pattern of plasma melatonin and progesterone concentrations in hair [Santa Inês (SI)] and wool [Romney Marsh (RM) and Suffolk (SU)] ewe lambs kept under natural photoperiods at 21 degrees 59'S, 12 ewe lambs (four/breed) were used. For melatonin, blood samples were collected monthly throughout the year at the onset (17:00, 19:00 and 21:00 hr) and end (04:00, 06:00 and 08:00 hr) of the night, and for progesterone the samples were collected in the morning, two to three times a week throughout the year. Plasma melatonin concentrations at different times of the day changed according to the season. In diurnal periods (17:00 and 8:00 hr) no seasonal differences were observed but they became evident in the nocturnal intervals (21:00 and 4:00 hr) and transitional night-day (6:00 hr) times. The patterns of melatonin secretion were higher in winter and autumn than in spring and summer. The patterns of plasma progesterone secretion were affected by interaction between breed and season. There was no seasonal variation in plasma progesterone concentrations for SI females. The progesterone pattern for RM and SU females varied with season. The plasma levels were higher in autumn and winter than in spring and summer. At 21 degrees 59'S hair and wool ewe lambs showed the same annual pattern of plasma melatonin concentration while the annual progesterone profiles were quite different. For SI females this pattern was constant along all seasons and for RM and SU females this pattern was higher during autumn and winter than spring and summer.

Use of nonergot alkaloid-producing endophytes for alleviating tall fescue toxicosis in sheep

Nonergot alkaloid-producing endophytes from New Zealand were inserted into tall fescue (Festuca arundinacea) cultivars in an attempt to address the problem of fescue toxicosis in grazing sheep. A 3-yr grazing study was conducted to determine lamb performance and to evaluate toxicosis in lambs grazing nonergot alkaloid-producing endophyte-infected (AR542 or AR502), endophyte-free (E-), or wild-type toxic endophyte-infected (E+) Jesup tall fescue or nonergot alkaloid-producing endophyte-infected (AR542) Georgia-5 tall fescue. Replicated 0.11-ha tall fescue paddocks were established at the central Georgia Branch Station during September 1997 and stocked with lambs from spring 1998 through autumn 2000. Mean ergot alkaloid concentrations were higher (P < 0.01) in E+ forage than in AR542, AR502, and E- tall fescue, and ergot alkaloid concentrations in E- plants and plants infected with AR542 and AR502 were low. Forage availability did not differ (P = 0.92) across treatments during autumn and was higher (P < 0.05) in Georgia-5 AR542 than in Jesup AR502 and E+ pastures. Initial serum prolactin (PRL) concentrations did not differ (P = 0.58) across treatments during autumn, but were higher on Jesup AR542 than E+ during spring. Post-treatment serum PRL concentrations were depressed (P < 0.01) on E+ compared with AR542, AR502, and E- in both spring and autumn. Signs of heat stress were observed in E+ lambs during periods of high ambient temperatures. Mean post-treatment rectal temperature and mean stocking rate exhibited treatment x year interactions (P < 0.05). Lamb ADG was higher (P < 0.05) on AR542, AR502, and E- than on E+ tall fescue. Similarly, gain/hectare was higher (P < 0.015) on AR542, AR502, and E- than on E+. Tall fescue pastures containing AR542 and AR502 endophytes yielded lamb performance that did not differ from that on E- tall fescue and which was superior to performance on E+ tall fescue. Depressed PRL concentrations and elevated rectal temperatures as indicators of toxicosis were evident only in lambs grazing E+ tall fescue, suggesting that nonergot alkaloid-producing endophyte-infected tall fescue is a viable alternative for alleviating tall fescue toxicosis.