The transition period is normally defined as the last three weeks of the dry period and the first three weeks of lactation.
A large number of changes take place during this time, including a reduction in food intake, changes in hormone levels, social changes (joining a new group and adopting to a new routine), and changes in diet type and quality.
These changes combine to make the transition period a time of ‘stress’ for the cow, and as a consequence, the cow’s immune system becomes suppressed making her more susceptible to infections. Diseases which occur during this time can have a long term impact on cow performance during the following lactation.
Nutrition and management strategies during the transition period should seek to minimise stress, and the extent to which the immune system is suppressed. From a nutritional perspective, while cows have a relatively low energy demand during the dry period, they may not be able to meet this requirement during the last few weeks pre calving.
In addition, energy demands increase dramatically post calving, and most cows are unable to consume enough energy to meet their requirements during early lactation. This places cows in a ‘break-down’ mode whereby they utilize fat stores to supply the additional energy needed – commonly termed milking ‘off her back.’ As cows mobilise these fat stores, fatty acids and ketones begin to circulate in the blood stream, and these are known to have a detrimental effect on the cow’s immunity.
The potential benefits of offering concentrates during the dry period are subject to much debate. For example, it is often suggested that concentrate feeding during the dry period helps cows gain body condition, and prepares the rumen to deal with a concentrate based diet post calving.
This might improve the cow’s immune status. However, if concentrate feeding in the dry period is excessive, cows will become overfat and previous research has shown that cows with a higher body condition score eat less after calving, mobilise more body tissue and this has a negative effect on immune function.
The objective of the current research at AFBI Hillsborough was to examine the effect of concentrate feeding during the dry period on the performance and immune function of dairy cows. The research programme was co-funded by AgriSearch and DARD.
This study involved 51 Holstein-Friesian dairy cows. Cows were managed on one of two feeding strategies during the dry period:
l Silage only: cows on this treatment were offered grass silage (plus a dry-cow mineral/vitamin mix) throughout the dry period.
l Silage plus concentrates: cows on this treatment were offered grass silage (plus a dry-cow mineral vitamin mix), plus approximately 3 kg concentrate per cow per day throughout the dry period.
All cows were offered a moderate quality third cut silage during the dry period (dry matter, 24.7 %; crude protein, 14.4 % DM; metabolisable energy, 10.5 MJ/kg DM), while the concentrate offered with the Silage plus concentrates treatment had a crude protein content of 16.6 % (fresh basis). Following calving cows on both treatments were managed identically for a 10 week period, and were offered a total mixed ration comprising of grass silage and concentrates, mixed in a 40:60 ratio on a DM basis.
Cows on the Silage only treatment had a lower dry matter intake during the dry period than those offered concentrates, and also experienced a greater reduction in intake during the last few weeks pre-calving (Figure 1). In addition, the energy intakes of cows on the Silage only diet was insufficient to meet their energy requirements during the two weeks pre calving. As a result of their higher intakes, cows on the Silage plus concentrate treatment gained more liveweight (Figure 2) and body condition during the dry period than those on the Silage only treatment. However, neither calving difficulty nor calf birth weight was affected by dry cow management.
Following calving, feed intakes were unaffected by concentrate feeding during the dry period. However, cows offered concentrates during the dry period lost more liveweight and body condition than those on the Silage only treatment.
The effects of concentrate supplementation during the dry period on cow performance during the first 10 weeks of lactation are summarized in Table 1.
While neither milk yield nor milk protein content was affected by concentrate feeding during the dry period, cows offered concentrates tended to produce milk with a higher fat content. This is likely to reflect the increased mobilization of body fat with cows on this treatment.
As already discussed, the risk of disease increases during the dry period, especially mastitis and ‘calf-bed’ infections. White blood cells are one of the main parts of the immune system which deals with bacterial infections, and these are particularly important during the transition period. The ability of these white blood cells to destroy bacteria was examined in this experiment on three occasions, namely at three weeks pre-calving, and at weeks one and two post-calving.
The white blood cells of cows offered the Silage plus concentrate treatment had an enhanced ‘bacteria killing ability’ during the first week post calving compared to those from cows offered the Silage only treatment (Figure 3). Nevertheless, this effect was relatively small, and no difference was observed in the incidence of disease between the cows on the two treatments.
Cows offered concentrates during the dry period gained more liveweight before calving but lost more after calving, than those offered a silage only diet. However, neither milk yield nor milk solids yield was affected by concentrate feeding during the dry period.
While cows offered concentrates had an improved immune defence against bacteria during the first week of lactation, this did not result in a reduced incidence of disease during this time.
If moderate to good quality silage is offered during the dry period, there is no economic response to concentrate feeding at this time.