These questions were addressed in a study by Dr Silva-del-Rio and colleagues in a study published in 2010 in the Journal of Animal Science, Volume 88, pages 1048 to 1060. The title of the paper appropriately was Effects of twin pregnancy and dry period feeding strategy on milk production, energy balance, and metabolic profiles in dairy cows.
It is well-known that cows bearing twins face greater challenges following the birth of the calves, amongst others being more prone to metabolic diseases and lower milk production than cows with single calves. However, correct feeding strategies may assist in ameliorating these problems. Normally in the US, cows in the dry period are fed low energy in the first two-thirds of the dry period to prevent unwanted body condition score gain, whereas during the three weeks before calving they are fed a moderate energy diet to maintain energy intake despite the drop in feed intake because of pressure on the rumen by the calf. This strategy was designed for cows carrying single calves and might not be optimal for cows carrying twins, because (1) the energy demands of pregnancy are 50 to 70% greater for twin-bearing cows, (2) feed intake drops even more in cows with twins, and (3) cows with twins have a shorter gestation length of the order of five days, which effectively shortens the period where they receive the moderate energy diet. These factors of course increase the risk of fatty liver and ketosis in twin-bearing cows.
In this study, therefore, the authors investigated if a differential feeding strategy would mitigate the negative effects mentioned, by testing if providing the moderate energy diet for a longer period than three weeks before calving will help twin-bearing cows. The control feeding strategy was the normal procedure followed in the US whereas the test groups of both single and twin-bearing cows were fed the moderate energy diet for the entire dry period of 8 weeks. The results show that cows with single calves had slightly higher feed intakes before birth of the calf than cows with twins, but body condition score did not differ; neither did it differ between the normal feeding strategy and the 8 weeks of moderate energy test period. As expected energy balance was greater for cows with single calves and for cows fed the moderate energy for 8 weeks than for 3 weeks. Twin-bearing cows, even in the 8-week group still showed more risk for metabolic disease before calving. Interesting, though, after calving cows with twins were in a more positive energy balance than cows with single calves. This is partially explained by the lower milk production of the cows with twins. The 8-week groups also had higher milk yields than the 3-week groups irrespective of whether the cows bear twins or singles. The respective milk yields were 50.8 kg and 45.5 kg per day for the 8-week and 3-week groups of cows with single calves, and 46.9 kg and 42.9 kg per day for the 8-week and 3-week groups of cows with twin calves. The response to feeding a moderate energy diet for 8-weeks was therefore independent of pregnancy type. This lead to the conclusion that feeding cows a moderate energy diet throughout the dry period is more beneficial than feeding the moderate energy diet for the last three weeks before calving which is the normal procedure. However, feeding after calving must be optimal in cows that have been fed the moderate energy diet during the entire dry period, since they are more prone to metabolic disturbances than cows receiving the moderate energy diet for only the last three weeks before calving.