"An exciting and growing body of scientific evidence supports the notion that the maternal environment in which foetuses develop plays a profound role in the development of the reproductive and other physiologic systems," write Drs Mark J. Estienne and Allen F. Harper of Virginia Tech's Tidewater AREC (TAREC) in the September 2008 issue of Livestock Update.

They explain that foetal programming refers to the process by which an acute or chronic stimulus in the uterus establishes a permanent response in the foetus that impacts physiological function later in life.

The concept of foetal programming in pigs was illustrated by O'Gorman and colleagues in 2007. They found that age at first oestrus was significantly delayed (by 14 days) in the female offspring of sows that had been subjected to stress during pregnancy.

Previous work by Estienne and colleagues at TAREC showed that the pregnancy rate was higher for gilts housed in individual stalls (100%) than group-housed individuals (85.7%) although the stress level appeared to be higher in the gilts kept in stalls. They measured stress as the concentration of cortisol in the blood serum.

For their latest trial, Drs Estienne and Harper put forward the hypothesis that if there is a real difference between housing systems (individual stalls versus group pens) in terms of 'stress' or welfare of the sow, then foetal programming would lead to differences in growth and reproductive performance of the offspring. They looked at the growth and age a puberty of the female offspring.

Experimental Details

The researchers used Yorkshire x Landrace gilts mated by artificial insemination (AI) and allotted to one of three types of gestation housing:

1. individual stalls throughout pregnancy
2. group pens throughout pregnancy (5 to 6 gilts/pen) or
3. individual stalls for 30 days post-mating and then group pens for the remainder of pregnancy.

From then on, all gilts and their offspring were treated the same way, keeping the treatment groups separate. From weaning at about 25 days of age, the gilts were separated from the barrows. After 5 weeks in the nursery, the groups of gilts were transferred intact pens to the grower-finishing barn until they weighed around 240lbs (109kg). At this stage, their backfat thickness was measured. Records were kept at each stage of the animals' weight and feed intake.

After the grower-finishing phase, the gilts were checked for oestrus once daily in the presence of a boar and age at puberty, i.e. first standing oestrus in the presence of the boar, were determined. Ten days later, all gilts were killed and their reproductive tracts were evaluated.

Findings

There were no effects of dam pregnantly housing on litter size, although there was a tendency for a greater average number of pigs born alive for treatments 1 and 3 (11.8 and 11.4, respectively) compared to 9.2 piglets for treatment 2.

The body weights of the piglets were similar at birth, weaning and the end of the nursery phase.

Some differences between the groups emerged during the growing-finishing period, as shown in Table 1. Overall, average daily gain was not affected by treatment. However, the pattern of pig growth was affected by housing of the dams: the offspring of gilts from treatment 1 weighed more during the last two weeks of this phase than the other treatments.

There was no effect of treatment on feed intake but feed conversion was significantly better (P<0.05) in gilts from treatments 1 and 3 than treatment 2. Pigs from treatment 1 tended (P<0.09) to have less back fat than those from treatment 2, with treatment 3 being intermediate.

Investigations of the reproductive tracts showed that the average weight of ovaries (P=0.07) and the weight of follicular fluid (an indication of follicle number and/or size; P=0.08) tended to be greater for gilts from treatment 2.

Dam housing type during pregnancy did not affect the number of corpora lutea (an indication of ovulation rate), average size of corpora lutea or uterine weight.

The average age at puberty was similar for all the groups. However, for the period between 151 and 165 days of age, fewer (P<0.05) gilts from treatment 1 had reached puberty than the other two groups (Figure 1).

Figure 1. Cumulative percentage of gilts attaining puberty by various ages for gilts farrowed by females that were kept in different housing systems during pregnancy
^{Within an age range, means marked by different superscripts (a, b) differ (P<0.05)}

Discussion

Around 60 per cent of sows in the US are kept in individual stalls throughout pregnancy. The restricted freedom of movement is strongly criticised by animal welfare groups on the basis that this type of housing is stressful although a comprehensive review of the scientific literature concluded that well-managed stalls or group pens generally produce similar states of well-being for pregnant sows in terms of physiology, behaviour, performance and health.

This is the first report of the effects of the dam's housing during pregnancy on the performance of the offspring.

It illustrates that the type of housing to which pregnant gilts are exposed affects the performance of gilt offspring. Although there were no effects during the lactation and nursery phases, gilts farrowed by sows gestated in stalls grew faster than the other treatments during the late finishing phase. Gilts from females kept in stalls throughout pregnancy were leaner at market weight.

Gilts from dams housed in groups had larger ovaries, greater follicular development, and reached puberty sooner than did those from dams housed in stalls throughout pregnancy. In general, reproductive characteristics of gilts from dams that spent the first 30 days of pregnancy in stalls and were then moved to group pens were intermediate between the two other groups.

Drs Estienne and Harper conclude, "The type of housing to which pregnant gilts are exposed affects subsequent growth and reproduction in female offspring perhaps through a phenomenon referred to as foetal programming.

"In general, gilts farrowed by females kept in stalls during gestation grew faster and were leaner at market weight but displayed delayed puberty."

Although the mechanisms responsible are not yet known, the work provides further evidence of the concept of foetal programming, and may help producers considering a switch from individual to group housing in pregnancy.

Reference:

Estienne M.J. & A.F. Harper, 2008. Effects of type of sow gestation housing on growth performance and reproduction in gilt offspring. Livestock Update, September 2008.

Further Reading

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