The effect of lactation length on the circulating concentrations of progesterone and oestradiol in the early weaned sow.

Eighteen crossbred multiparous sows were allocated at random to one of two lactation lengths: 42 or 10 days. All sows were mated at the oestrus after weaning and from mating until day 26 post coitum they were bled every second day. Progesterone and oestradiol concentration in the plasma was determined by radioimmunoassay. Progesterone increased more rapidly between days 4 and 10 post coitum in early weaned sows and the oestradiol surge at mating was abnormally extended for the same group.

Effects of repeated challenges with exogenous oestradiol benzoate and progesterone on reproduction in prepubertal Hubei white and Meishan cross gilts.

Two experiments were carried out to investigate the effects of repeated challenges of oestradiol benzoate and progesterone on reproduction in prepubertal gilts. In experiment 1, 21 Large White cross (Meishan cross Landrace) prepubertal gilts were allocated to one of three treatments. Treatment A gilts were given oestradiol benzoate injections (15 micrograms kg-1 bodyweight) at 140 and 160 days old and daily injections of progesterone (20 mg day-1 per gilt) for four days, from day 12 after each oestradiol benzoate challenge. Treatment B gilts were given the same oestradiol benzoate and progesterone challenges but from 160 days onwards. Treatment C gilts were the controls and were given only oil injections. All the gilts were mated at their first oestrous period. In experiment 2, 45 prepubertal Hubei White gilts were allocated to the same treatments as used in experiment 1. The administration of oestradiol benzoate induced oestrus (52 of 64) and ovulation (51 of 64) in a high proportion of the gilts in both experiments. The proportions of gilts which had regular oestrous cycles (within 10 days after progesterone withdrawal) were 0.82 (18 of 22) and 0.16 (3 of 19) in treatments A and B, respectively (P < 0.001).

Enzyme-linked immunosorbent assay for the measurement of immunoglobulin G concentrations in porcine plasma and colostrum.

An enzyme-linked immunosorbent assay is described for the estimation of porcine immunoglobulin G in either colostrum or plasma samples. The inter-assay coefficient of variation was 9.1 per cent and the intraassay coefficient of variation was 7.2 per cent. The repeatability or intra-class correlation coefficient of the assay was 0.9. The assay proved to be a sensitive, inexpensive and rapid method for assessing the immune status of pigs.

A rearing system for colostrum-deprived neonatal piglets.

A system for the artificial rearing of colostrum-deprived neonatal piglets is described. A total of 443 piglets in 6 batches was reared. Each piglet, immediately after birth was placed in a separate incubator which was ventilated with heated filtered air. Piglets were fed hourly by an automatic system and were offered a liquid milk substitute. The mean survival rate up to the time piglets were transferred out of the rearing unit at 2 weeks of age was 78 +/- 7%. The mean daily live weight gain up to 2 weeks of age was 148 +/- 16 g/day and the dry matter intake over the same period was 154 +/- 10 g/day per piglet.

Attempt to control parturition in the sow using an oral progestogen.

Analogues of prostaglandin F2 alpha are widely used in the United Kingdom to induce parturition in sows. A disadvantage is that sows are induced to farrow in advance of expected delivery dates. An alternative might be to maintain gestation by the application of a progestogen. Farrowing might then be initiated on the withdrawal of the progestogen. The use of an orally active progestogen (allyl-trenbolone) in an attempt to control the time of parturition in sows is described. In experiment 1, 20 large white cross landrace sows were allocated at random to one of two treatments. Treated sows were fed 16 mg/day of allyl-trenbolone from day 111 of gestation to day 118 of gestation. The farrowing performance of these sows was compared with that of control sows which farrowed naturally. Treated sows farrowed significantly (P less than 0.01) later than the control sows (118.2 and 116.1 days respectively). For treated sows the interval from progestogen withdrawal to farrowing was 29.6 +/- 4.8 hours. The number of stillbirths for treated and control sows respectively was 2.1 and 0.4 per litter. Treatment had no effect either on the birth weight of piglets or on their weaning weight at six weeks old. There was a tendency for more treated sows to show subsequent reproductive malfunction. In a second experiment, under commercial conditions, 81 sows and 12 gilts were allocated to one of four treatments. Treatment A animals were untreated controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of oestradiol benzoate injections, exposure to the boar and age on the attainment of puberty in the gilt.

Thirty large white cross Landrace prepubertal gilts from five litters were allocated at random within litters to one of six treatment. All the gilts were given three daily intramuscular injections of 6 micrograms/kg liveweight of oestradiol benzoate but the first injection was given at either 100 days, 120 days, 140 days, 160 days, 180 days or 200 days old. From the time the first oestrogen injection was given, until the end of the experiment, the gilts were allowed daily contact with a boar for 20 minutes. The gilts were mated with a mature boar at the appearance of the second oestrus and they were slaughtered 20 days later. The numbers of gilts ovulating in the treatment groups were determined from plasma progesterone concentrations measured twice weekly throughout the experiment. The numbers of gilts ovulating within 10 days of the oestradiol benzoate injections were 3 of 5, 1 of 5, 0, 0, 3 of 5 and 1 of 5, respectively, in the groups first treated at 100 days, 120 days, 140 days, 160 days, 180 days and 200 days old. For those gilts which were successfully mated, no significant differences were observed between the treatment groups in the number of viable embryos per gilt.

Control of oestrus and ovulation in peri-pubertal gilts with allyltrenbolone or a combination of natural gonadotrophins.

One-hundred-and-twenty large white X landrace gilts were allocated at random to one of three treatment groups. Treatment A gilts were given an orally active progestogen, allyltrenbolone (Regumate; Hoechst UK) once daily for 18 days from 185 days of age. Treatment B gilts were given a subcutaneous injection of gonadotrophins (400 iu pregnant mare's serum gonadotrophin, 200 iu human chorionic gonadotrophin). (PG600; Intervet Laboratories) at 203 days of age. Treatment C gilts received no exogenous hormones. All the gilts were housed in groups of 10 from 153 days of age, and up to 203 days of age were isolated from boars. From 203 days each group of 10 gilts was subdivided into two groups of five, a boar was accommodated in a pen adjacent to each group of five and daily contact with it was allowed for one hour. Eight gilts in treatment A, five gilts in treatment B and seven gilts in treatment C failed to exhibit oestrus before 233 days of age (P greater than 0.05). The intervals from exposure to the boar to the onset of oestrus for treatments A, B and C were 8.5, 5.5 and 11.0 days respectively (P less than 0.001). Gonadotrophin treatment significantly reduced the time taken by gilts to show oestrus and the variability within the group was significantly less than that in the other two groups. There were no significant differences between the groups in the mean size of their litters.

Studies in sow reproduction: 4. The effect of level of feeding in lactation and during the interval from weaning to remating on the subsequent reproductive performance of the early-weaned sow.

PIP: An investigation of the effects of level of nutrition, both in lactation and from weaning to remating, on subsequent litter size and associated reproductive characteristics in the early-weaned sow is reported. Subjects were 75 sows in 5 groups. In 4 of the groups the sows were weaned after a 10-day lactation period. Group 5 was weaned following a 42-day gestation. The control group was fed up to 6.3 kg/day during lactation and 2.7 kg/day from weaning to remating. The 4 early-weaned groups were each fed differently. In lactation and during the inverval from weaning to remating they were fed either 2 or 4 kg/day. The group receiving only 2 kg/day during each period lost more weight than the others (p less than .05). Weight loss in lactation was significantly (p less than .001) affected by feeding. Sows weaned after a 10-day lactation period farrowed 2.7 piglets/litter less in the next parity than sows weaned after a 6-week lactation period. Weight losses during lactation were not related to subsequent litter size. Level of nutrition from weaning to remating in these tests had no influence on subsequent litter size. The early-weaned sow, even with large fluctuations in weight change over the period from parturition to remating, did not alter their ceiling for litter size. It seems unlikely that ovulation rate is the major factor limiting litter size in the early-weaned sow. Results suggest that embryo mortality following ovulation and coitus is increased in the early-weaned sow and that this effect then manifests itself as a ceiling to subsequent litter size.^ieng

Studies in sow reproduction: 5. The effect of lactation length of the so w on the subsequent embryonic development.

PIP: The relative importance of factors causing a decrease in sow productivity with systems involving weaning of piglets under 3 weeks of age was studied. The observed reduction in litter size has been attributed to the ovulation rate or to embryo mortality. Subjects were 45 female pigs. 3 lactation lengths were tried: 7, 21, and 42 days. All sows were remated at the 1st postweaning estrus and slaughtered 20 days later to determine ovulation rate and embryo survival. All were fed 1.8 kg/day during gestation. During lactation, the feeding level was increased to a maximum of 6.3 kg/day depending on the number of piglets. Feed level from weaning to remating was 2.7 kg/day. Blood samples taken on 5 occasions from weaning to slaughter were assayed for progesterone. The weaning to estrous interval increased from 6.1 to 8.2 days when lactation length was reduced from 42 to 7 days. Ovulation rates, as determined by luteal count, were similar for the different periods of lactation. Numbers of viable embryos decreased significantly (p less than .05) as lactation length was reduced from 42 to 7 days. The survival of those embryos present decreased also (p less than .01). Embryo mortality increased from 17.3 to 40.4% when the lactation period was reduced from 42 to 7 days. Ovarian weights, uterine weights, and average embryo spacing were the same in all 3 groups. Plasma progesterone levels were low at weaning and remating, higher at 2 days postcoitum, and maximum at 10 days postcoitum. Between treatment groups, plasma progesterone levels were similar but varied markedly within treatment groups. Since ovulation rates were shown to be similar, this factor was eliminated. The interval from weaning to estrus was not considered important. Litter size was shown to be a major limiting factor. Embryo survival during the early period of gestation was shown to be the most important factor in limiting productivity.^ieng

Effects of geographic transfer on the timing of seasonal breeding of rhesus monkeys.

This is a study of the effects of geographic transfer on the timing of seasonal breeding of free-living rhesus monkeys on Cayo Santiago and La Parguera islands in Puerto Rico. The results demonstrated a progressive shift in the breeding season of the transferred group. The full shift required a period of 2 years. Change from one environment to another produced shifts in onset of estrous. The explanation for this phenomenon proposes an interaction between the specific reproductive state of the female, which may or may not be sensitive to a particular environmental change, and the environmental variation which is correlated with onset of breeding.