Influence of Cross-fostering on Piglet Growth and Survival

Introduction

Cross-fostering to equalize birth-weight within litter and accommodate individual sow rearing capacity reduces preweaning mortality.

However, it is important to implement cross-fostering correctly. When pigs are cross-fostered after 3-days of age, the disruption of the newly established teat order will likely result in reduced piglet weight gains and increase preweaning mortality. For this reason, it is usually recommended that cross-fostering be complete by 3-days after farrowing.

However, even this period may be too long. It has been shown that antibody content of colostrum will decrease more than 50% within 12-hours of farrowing. Therefore, if newborn piglets are fostered onto a sow that had farrowed more than 12-hours previously, their passive immunity will be compromised.

Further, survey evidence derived from PigCHAMP indicates that preweaning mortality is increased when greater than three piglets are fostered onto a sow. It is apparent that further work is warranted to examine the effects of cross-fostering on piglet performance.

Trial

We induced 120 mixed parity sows to farrow with cloprostenol. At farrowing, the piglets were weighed and the lightest (L) 50% from two litters were placed on one sow and the remaining heavier pigs (H) on another.

A third sow served as a litter-intact control (I) and no pigs were cross-fostered. Cross-fostering was completed within 12-h of birth. Pigs were weighed again at 3-d and at weaning. Pig performance was assessed on the basis of survival and preweaning growth rate.

Comparisons were made between litter weight designations (H, L and I) and between H and the heavier half of intact litters (I-heavy) and between L and the lighter half of intact litters (I-light).

Results and Discussion

There was a significant sow effect on preweaning piglet growth and survival (P &ls; 0.001). The effects of cross-fostering on piglet preweaning growth and survival and a comparison between intact litters and the heavier and lighter halves of the intact litters are shown in Table 1.

There was no significant advantage or disadvantage for cross-fostered pigs. Weight gain between days three and weaning was not affected by litter weight. Post-weaning ADG was not affected by litter weight. Patterns of preweaning survival were as expected with the heavier pigs having the least mortality and this was unaffected by cross-fostering. We conclude from these data that the creation of light birth-weight litters does not increase or decrease preweaning survival.

Table 1. The Effect of Cross-fostering on Piglet Growth and Survial

NS = no significant difference across the row; numbers within a row, marked by different letters are significantly different Roy Kirkwood, Louisa Zak and Laki Goonewardene

Can We Make Sows Ovulate at the Time of Farrowing?

Short lactation lengths are associated with reduced sow fertility. One aspect of this reduced fertility is a longer and more variable wean-to-estrus interval. The Alberta Pork Research Centre is interested in finding and evaluating new methods to control and synchronize post weaning estrus.

We know that for about 30 hours after farrowing, the sow's ovary has many large follicles and that her hormonal system is very active. A new method of estrus synchronization that we have evaluated is causing sows to ovulate at the time of farrowing with an injection of 1000 IU hCG (human chorionic gonadotropin). hCG is one of the components of PG600. If we can induce ovulation at farrowing, the sow will go through an estrous cycle and return to estrus about 21 days later, regardless of when she is weaned.

We injected sows with hCG at various times relative to farrowing and then determined whether sows had ovulated based on blood progesterone concentrations. A value greater than 5 nanograms (ng) of progesterone per mL of serum indicates ovulation. A value between 2 and 5 ng per mL suggests a partial effect and values less than 2 ng per mL indicates ovulation did not occur.

We initially treated 8 sows at 24 hours after farrowing. Based on blood progesterone concentrations 7 days after farrowing, none had ovulated.

We then injected a further 35 sows sooner after farrowing. This meant that if a sow farrowed overnight, she was treated immediately the next morning. If she farrowed during the day, she was treated last thing in the afternoon. Of these sows, 17 (48.6%) ovulated.

In an attempt to determine the best time to administer the hCG, we divided another 26 sows among the following treatments with the following results (Table 1).

Table 1. The Effect of hCG Injection on Ovulation

These results demonstrate that the sow's ovulatory response to hCG at farrowing is far too unpredictable to be of commercial application.

Roy Kirkwood and George Foxcroft