Introduction

Sow longevity is a key component of an efficient and profitable pig farming enterprise. However, the sow culling rate is steadily increasing at a rate of between 0.7 per cent and 1.0 per cent per year and currently stands at 50 per cent, indicating that the longevity of Irish sows is declining.

Efforts to improve sow longevity should be aimed at the replacement animals, which are under-valued on many units. They need to be managed, housed and fed appropriately during the developmental phase to ensure that they are at a high level of health and are both physiologically and behaviourally mature on entry to the breeding herd.

A farm survey of lameness found that farms that housed gilts separately from finisher stock had a reduced risk of lameness in the replacement gilts and in the pregnant gilts and sows. The author and her colleagues also found that the earlier gilts are managed separately to the finishers the larger the reduction in lameness (Figure 1).

Figure 1. The proportion of lame gilts that were housed separately from finisher stock at various weights

Inappropriate nutrition during the developmental phase can contribute to the problem of lameness in replacement gilts. Many producers feed their replacement gilts one of two feeding regimes; a finisher diet to service or a gestation sow diet from 100kg until service. Such regimes may not be optimum for the developing gilt; finisher diets are formulated for fast growth rates and high lean meat deposition and a gestating sow diet is formulated for a sow that has finished growing.

In contrast, diets specifically formulated for the developing gilt take into account the nutritional requirement for bone development and fat deposition. High growth rates are linked with several pig welfare issues including osteochondrosis, leg weakness, postural defects, cardiovascular issues, increased skeletal injuries, modification of the release of various hormones and behavioural modifications. Replacement gilts require higher levels of calcium and phosphorus for bone mineralisation to prevent bone weaknesses and as a backup source of calcium and phosphorus for the litter requirement if needed during gestation and lactation.

Studies suggest that trace minerals such as zinc, manganese and copper are crucial to hoof health. Zinc is essential for cellular repair and replacement and therefore increases the rate of wound healing. Copper is essential in the development of antibodies and the replication of lymphocytes, while manganese is vital for the formation and maintenance of cartilage and bone. Copper deficiency is associated with joint stiffness and enlargement, and weak or short bones.

The dietary supplement Availa Sow® (Zinpro) contains trace amounts of organic zinc, copper and manganese in a structure that makes the minerals more bioavailable than other forms, thus easier to absorb and utilise. Inclusion of Availa Sow in the diet of breeding sows reduces heel erosion, heel overgrowth and white line lesions in sows and in one study reduced the removal rate of young sows from the herd (up to parity 3) by 20 per cent.

Two experiments were conducted at Moorepark to determine the effect of feeding a gilt developer diet on indicators of lameness in group housed replacement gilts.

Study 1: Limit-Feeding a Developer Diet

Limit-feeding a gilt developer diet has the potential to reduce weight gain while providing the requirements of bone and claw development and maintenance and may result in improved locomotory ability and overall limb health when compared to the two most common feeding regimes.

In the first experiment, 36 Large White × Landrace gilts were selected, housed individually and assigned to one of following dietary treatments; finisher, gestating sow and developer, at 65kg (Table 2). The dietary composition of the three treatments is detailed in Table 3.

The experiment lasted 12 weeks and the gilts were then slaughtered at around 140kg, which was the target weight that corresponded to service. None of the gilts was lame when entering the experiment however, the researchers found that, from the fifth week of the trial onwards, there were more lame gilts on the finisher and gestating sow dietary treatments than on the developer treatment (Table 4).

They also found that by week 12, gilts on the developer treatment had a lower occurrence of claw lesions than the finisher and gestating sow treatments (Table 5). Additionally all gilts on the finisher and gestating sow treatments had uneven claws by week 12. Interestingly, on the developer treatment, the proportion of gilts with uneven claws reduced as the trial progressed from 90.9 per cent to 27.3 per cent. These improvements in claw health may be attributed to the inclusion of the zinc, copper and manganese supplement, Availa Sow in the developer treatment.

In addition, gilts on the developer treatment were found to have lower surface lesion scores on the elbow joint than gilts in the gestating sow and finisher treatments (Table 6).

It should be noted that gilts on the finisher treatment had the highest incidence of osteochrondrosis dessicans (OCD; score 5). Also observed were differences in weight gain at weeks 4 and 10, with gilts on the developer treatment weighing less than gilts on the finisher and gestating sow treatments (Figure 2). This reduction in weight gain in the developer treatment may have contributed to the reduced joint lesion scores as fast weight gain is a known risk factor for joint lesions. No effects of treatment were found on limb lesions, bone mineral density (BMD) and carcass characteristics.

Figure 2. Average body weight of gilts on three treatments at day 0, week 4, week 10, week 12 in study 1

Study 2: Ad libitum Feeding a Developer Diet

Several advantages for pig locomotory health were detected when gilts were restricted fed a developer diet. However, on most farms replacement gilts are currently fed ad libitum so switching to a restricted feeding regime could be costly. Therefore the author and her colleagues decided to investigate if the same benefits to locomotory health of limit-feeding a developer diet could be seen when ad libitum feeding the same diet.

In this experiment, 180 Large White &times Landrace gilts were housed in 18 pens and assigned to the finisher, gestating sow and developer dietary treatments, from 65kg to 140kg over a 12-week period and fed according to Table 7. At selection, four focal pigs per pen were identified for more detailed measurements.

It was found that from weeks 5 to 8 and 9 to 12, more gilts were lame on the finisher and gestating sow dietary treatments than on the developer treatment (Table 8).

By week 12, gilts on the finisher and gestating sow treatment had more claw lesions than gilts on the developer treatment but there was no effect of treatment on uneven claw size (Table 9). These improvements in claw health could be attributable to the inclusion of the zinc, copper and manganese supplement, Availa Sow in the developer treatment.

In an ad-libitum group feeding situation, there was no effect of treatment on joint lesion scores, bone mineral density, body weight, lying behaviour or on carcass characteristics.

Ad libitum feeding a diet specifically formulated for developing gilts from 65kg reduced lameness and claw abnormalities. Joint lesion benefits were not observed in this situation. The lack of a difference in weight gain between treatments may explain no difference in joint surface lesions in this scenario.

In conclusion, feeding a diet specifically formulated for developing gilts from 65kg reduced lameness when both limit- and ad libitum-fed when compared to the two most commonly practised feeding regimes. Gilts limit-fed a developer diet showed reduced claw abnormalities and joint surface lesions of the cartilage in the elbow joint. Gilts that were ad libitum fed a developer diet showed reduced claw abnormalities.

Ad libitum feeding a developer diet did not affect weight gain and as a result, may have resulted in no difference in joint surface lesions between treatments. The improvements observed would be expected to translate into improved welfare, longevity and productivity of the breeding herd.

Key Findings

Restricted feeding of a diet specially formulated for developing gilts from 65kg:

• reduced lameness
• reduced claw lesions
• reduced joint surface lesions of the humeral condyle
• had no effect on time to reach target weight.

Ad libitum feeding of a diet specially formulated for developing gilts from 65kg:

• reduced lameness
• reduced claw lesions
• had no effect on joint lesions
• had no effect on growth rate.

Key Recommendation

House gilts separately from finisher stock and feed a diet specially formulated for gilt development (restrictively, if possible) from 65kg or earlier.

Further Reading

Go to our previous article from this event by clicking here.

September 2013