An attempted intervention to solve a problem of lightweight pigs at weaning

Abstract

The presence of a high proportion of lightweight pigs (< 4.5 kg) at weaning was identified as a problem on a 600-sow farrowing operation. An intervention strategy involving special care pens where underweight pigs were fed milk-replacer and transitioned to a commercial grain-based starter diet was evaluated and found to be of limited benefit.

Case description

A problem of slow growth rate during the nursery phase was identified on a 600-sow farrow-to-feeder swine operation in which pigs are raised without antibiotics (RWA). There are 4 farrowing rooms consisting of 24 farrowing crates per room on this farm and farrowing rooms are operated on a strict all-in/all-out basis with weekly weaning. The average age of pigs at weaning is about 3 wk. Eight nursery rooms are located in the same barn as the farrowing rooms and breeding-gestation area. The nursery rooms consist of 8 pens holding approximately 30 pigs each. The rooms are also operated on an all-in/all-out basis with thorough cleaning between fills.

In order to accurately assess nursery performance, 1 batch of pigs (n = 240) was observed from weaning until shipment to the grower/finisher barn. These pigs were ear-tagged and weighed individually at weaning and at exit from the nursery 7 wk later. For the purpose of this study, underweight pigs were defined as those weighing < 4.5 kg at weaning. This value was selected because companies in the swine industry use this weight as a cut-off for accepting pigs into a nursery. During the pigs’ 7 wk in the nursery, daily health observations were recorded to account for morbidity within the batch and pigs’ tag numbers were recorded if they died, were culled, or became sick. The average [± standard deviation (SD)] weaning weight of the batch (n = 240) was 6.0 ± 1.6 kg, and the mean nursery exit weight (n = 236), omitting those that died prior to exit, was 22.8 ± 4.3 kg. This resulted in a mean total weight gain of 16.8 ± 3.7 kg within the nursery over the 7 wk, with a mean daily weight gain of 0.35 ± 0.08 kg. Furthermore, there were 13 recorded cases of illness and 4 mortalities, and 41 (17%) pigs were classified as “underweight” (< 4.5 kg) at the time they entered the nursery. Pigs that entered the nursery as underweights continued to be smaller than the other pigs throughout their stay in the nursery. The weight of the underweight pigs at the end of the nursery period was significantly less [19.1 ± 3.7 kg compared to 23.5 ± 4.0 kg, (P < 0.05)] than the rest of the nursery pigs. No underweight pigs died during the 7 wk in the nursery.

The results from tracking this batch of pigs through the nursery confirmed that slow growth rate was a problem. The average daily gain (ADG) in the nursery from 3 wk of age to 10 wk of age was 0.35 kg/d for this batch of pigs, which is well below the industry standard of about 0.43 kg/d (1,2). The standard growth for weanling pigs on farms adhering to an RWA program is slightly lower (0.41 kg/d) (3), but the ADG on this farm was clearly below this level as well. It was felt that the underweight pigs at weaning were contributing significantly to this poor overall growth rate. To combat this problem, a strategy was devised to provide special care for these lightweight piglets for the first 2 wk after weaning in order to help them to transition to solid feed and to gain weight more quickly. All non-underweight pigs were weaned normally, and spent 7 wk in the nursery under the producer’s regular care, which included ad-libitum feeding of a commercial starter crumble diet for about 3 d, a second stage mash diet for 10 d, and finally, a third stage starter soy-corn mash diet mixed on-farm. In contrast, lightweight pigs at weaning were placed in a separate room equipped with 2 floor feeders (fastened to the slatted floor), 2 tank feeders (fastened to the pen wall), and water nipples providing ad-libitum water. For the first 6 d, 1 floor feeder was filled with creep feed (Natures Blend Piglet #1 Starter Pellets; Grand Valley Fortifiers, Cambridge Ontario), and the milk supplement (Supp-Le-Milk; Soppe Systems, Manchester, Iowa, USA) was divided between the 3 other feeders. During the following 4 d, the pigs were fed a milk-mash diet in 1 of the floor feeders, consisting of milk replacer mixed with the solid starter feed, to aid in the transition towards a solid diet. The milk supplement was diluted with water over these 4 d in the tank feeders, with the ratio of milk supplement to water being halved. In the final 4 d, the pigs received a diet of only solid nursery feed.

After 2 wk in the special care pens, the pigs were individually weighed and moved to the nursery, where they were re-united with their initial weaning batch of pigs, but placed in a separate pen. The pigs were housed in the nursery for the remaining 5 wk under the producer’s regular care, with no additional intervention. This procedure of providing special care to assist the lightweight pigs in transitioning to the nursery was performed on 2 separate batches using 30 pigs per batch. These 60 pigs were weighed at exit from the nursery and the growth rate of the pigs receiving special care was compared to the growth rate of underweight pigs in the previous batch in which underweight pigs received no special care. Six pigs in the special care group were removed from the analysis because they were considered extremely underweight (< 2.3 kg) and in retrospect the farmer would have ordinarily euthanized these pigs prior to weaning. The average weaning weight of the remaining 54 pigs was 3.4 ± 0.6 kg, which was not statistically different from that of the underweight pigs in the previous batch with a weaning weight of 3.5 ± 0.6 kg (P = 0.44). At the end of the nursery the mean weight of the underweight pigs that received extra care was 20.0 ± 4.0 kg resulting in an ADG of 0.40 ± 0.10 kg, which was not statistically different (P = 0.28) from the growth rate of the lightweight pigs in the early batch that was monitored but not provided with assistance. The farm manager decided not to institute the special care intervention because the rewards did not seem to warrant the extra labor and costs and did not solve the overall slow growth rate problem.

Discussion

Weaning is a stressful time in a pig’s life and various studies show that heavier weaning weights tend to result in better nursery pig performance (4–6). Litter size is dramatically increasing, particularly in Europe but also in Canada, so piglet weaning weights will almost certainly decrease and create a challenge for nursery management. Average daily gain in the nursery is directly related to weaning weight (7). Pigs that are underweight at weaning and that grow slowly in the nursery cause large size variation within batches of pigs being transferred to the grower-finisher stage (5). This was observed on the farm of interest, as 17% of pigs in 1 batch were underweight at weaning and these pigs had a mean weight at the end of the nursery stage of 19.1 ± 3.7 kg compared to 23.5 ± 4.0 kg for the pigs weaned at > 4.5 kg. This issue is of particular interest because weight variation is an important factor downstream in production, as poor weight gain in pigs at weaning continues to affect these pigs until they reach market weight (4–6). This ultimately cumulates in compromised production throughput, weight penalties at market, reduced barn flow, and disruption in overall herd health (8).

A major component of this lowered weight gain can be attributed to the changes occurring in a pig’s digestive tract during weaning, especially at younger ages (9). Due to a sudden lack of milk intake and minimal feed consumption during this stage, the intestinal villi begin to atrophy, resulting in reduced villus height and increased crypt depth (10). The integrity of the epithelium of the small intestine also becomes weakened, which reduces its barrier function and causes the entry of toxins into the blood and local inflammation (11). This also applies to the infiltration of various pathogens across the intestinal epithelium, as it increases the likelihood of these pigs developing mucosal inflammation, sepsis, or disease (9). The introduction of soybeans into the pig’s diet at weaning can also aggravate the gut, causing inflammation as well as reduced villus height (12). Overall, these changes in the pig’s gut result in decreased digestion and absorption of nutrients from their diet, causing reduced weight gain and increasing the risk of developing illness, such as malabsorptive diarrhea (13).

The intervention of special care pens using milk replacer and specialized feed to help small pigs transition to a grain-based nursery diet is a common recommendation to help disadvantaged underweight piglets at weaning. This method of supplementing pigs at weaning with milk has been recommended by many experts (14–16). Their studies involving supplementing pigs at weaning with additional dietary components, including milk and/or milk-replacer, revealed that villous height and crypt depth can be maintained when pigs do not experience nutritional stress at weaning (14–16). By reducing this stress, villous atrophy is prevented, resulting in maintained feed intake and continuous weight gain.

Although pigs receiving the extra care exited the nursery numerically about 1 kg heavier compared to underweight pigs receiving no additional care, this increase in exit weight did not prove to be statistically significant, which is similar to the findings of Mahan and Lepine (5). It is possible that a larger trial may have shown that this relatively small improvement due to the intervention may be significantly different, but it would still be economically difficult for the farmer to justify. The average price of a feeder pig exiting the nursery is about $2.50 per kg (17), so the return from providing special care, including milk supplement, housing and feeding equipment, and extra labor, was not cost-effective under the conditions of this study. Furthermore, it was proven that pigs not receiving this extra care fared well on their own without the need of supplementation, as they were only 1 kg lighter on average. However, these pigs are at risk for potential gut damage as a result of the lack of a dietary transition, which is accounted for in the special care program. Thus, there is a possibility that the intervention technique of special care and a transition diet might help to reduce the likelihood of a sudden outbreak of disease. If multiple batches of weaned pigs were followed, some receiving special care and other batches receiving no extra attention, a difference may have been noted if a few batches were affected with serious post-weaning diarrhea or other diseases. However, this farm did not have a history of disease outbreaks but did experience consistent slow growth in the nursery.

In conclusion, the farmer has been advised to continue handling underweight pigs as in the past and to abandon the use of special care rooms. Instead, efforts have been directed towards increasing weaning weights through improved milk production via improving sow feed intake and giving greater attention to creep feed consumption.