The importance of the dry period in dairy cows

To dry-off a cow means stopping milking for a certain period before the next calving. Usually, this interruption is at 220 days of pregnancy to ensure 60 days of production stop. Genetic selection in the last decades and the continuous attempts to obtain a calving-fertilization period as short as possible led to dry-off cows with very high milk yield. For these animals, the dry-off is at 235 days of pregnancy to reduce the daily milk production. According to the current scientific knowledge, a dry period shorter than 45 days or the lack of this pivotal time is inadvisable. Anyway, this period is a huge economic loss for farmers: a milk yield of 15 kg/day at 0.4 €/kg means 360 €/cow of lost revenue. So, why to dry-off the cows if they would produce until calving?

The most important reason for the dry period is to completely restore the hepatic function affected by the unavoidable negative energy balance of the first weeks of lactation (high amount of triglycerides accumulate in the liver compromising its functionality). The dry period is also useful to eliminate from the udder the pathogens accumulated during lactation.

In addition to these two main health reasons, during the last weeks of pregnancy, amino acids (both essential and not) and glucose are stored into body tissues as labile proteins and hepatic glycogen respectively as important reserves to draw upon after calving.

During the dry period, nutrient requirements are reduced because of the lack of milk production, but there are still maintenance and growth requirements. At the same time, the fetus is exponentially growing and the colostrum starts to be produced. In the central part of the dry period, primary or secondary energy deficits are rare, but frequently there are amino acids and other nutrients deficiencies (especially during the last 2 weeks). The fetus needs have the priority on those of the mother, so that it is difficult to find out deficiencies in the newborn, while they are frequent in the cows, even if in sub-clinical form. These deficiencies are important risk factors for metabolic pathologies.

For these reasons, it is important to ensure correct nutrition (both as nutrient intake and clinical/functional nutrition) in addition to good management of the animals and the environment during the dry period.

The dry-off

This first phase of the dry period is also the most delicate of the whole animal productive cycle and lasts a few days. In best-organized farms, there is a physical place where the cows are regrouped at 220-235 days of pregnancy and where they are regularly milked until production is lower than 15 kg/day. To reach this aim, the cows receive only hay and straw instead of the milking diet, concentrates, and silage. In the past, there was also water restriction but this caused rumen problems. The regrouping and the dietary restriction cause huge stress in cows. At milking suspension, we want the higher macrophages and neutrophils possible in the mammary alveoli and good phagocytic activity against milk residues and bacteria in the udder. As the immune system requires glucose, amino acids, and anti-oxidant substances, the stress that the animals experience during the dry-off period affects its efficiency.

The early dry

This is the central part of the dry period and commonly lasts 28 days (in a 60 days dry period). If the dry period lasts 45 days, the early dry is not present to avoid an unuseful group and dietary change of only 17 days: in this case, there is the direct passage from the dry-off and the preparation to the parturition.

In the early dry period there are 3 fundamental recommendations:

• To administer a diet consistent with the recommended needs according to the Nutrient Requirements of Dairy Cattle (NRC, 2001; Table 1);
• To avoid every BCS fluctuation (both positive and negative);
• To guarantee a comfortable environment with free access to the external paddock, feed and water, and excellent management of summer cooling. According to the current knowledge, the photoperiod management (short day) is not applicable during the early dry.

Table 1: Nutrient requirements of Holstein dairy cows (live weight 680 kg, BCS 3.3). NRC, 2001

The close up

As well as the dry-off, the close-up needs complicated and not standardized management. During this period the animal experiences a huge hormonal and metabolic rearrangement with a strong reduction of the feed intake even due to the uterus size. During the last weeks of pregnancy, there are frequently a strong mobilization of body lipids and an increase of plasma ketone bodies. Management and nutritional errors during the close-up can lead to sub-clinical rumen acidosis and metabolic ketosis. This is also a risk factor for post-partum hypocalcemic syndrome, placenta retention, post-partum ketosis, pathological udder edema, puerperal metritis, and abomasal dislocation. Moreover, is in the close-up (and during the whole dry period) that we can condition the early resumption of ovarian activity after calving, highly correlated to the conception rate. A further deepening about this topic is available in our previous article (Functional nutrition helps to prevent the economic losses related to the transition period).

Functional nutrition during the dry period

The standard diet for the dry period is easy to prepare if the scientific indications are observed. Anyway, it is possible not to reach the goals of the dry period for many reasons: bacteriological healing of the udder, prevention of hepatic lipidosis, and the restoration of labile proteins, liver glycogen, and antioxidants stocks. In these cases, and when there is a high amount of post-partum metabolic pathologies and delayed resumption of ovarian activity, clinical and functional nutrition is useful. There are available data about the effect of the dry period on the udder health, indicating that this goal is not already reached. As an example, here below are reported some Italian data:

• From 2014 to 2019, the percentage of cows with healthy udder before the dry-off and after calving (< 200,000 somatic cells/ml) went from 47 to 52.8%: improving performance but still rather disappointing;
• The percentage of cows that recover during the dry period decreased from 23.1% in 2014 to 21.2% in 2019;
• The percentage of animals that experience mastitis or worsen the udder leukocytosis during the dry period was 20.9% in 2014 and 18.9% in 2019.

Moreover, scientific pieces of evidence are reporting that over 20% of nipples remain open during the dry period and the incidence of new mammary infections is 8-17%. Supplementation of injectable anti-oxidant molecules or in the rumen-protected form in the diet, for example, vitamin A and vitamin E, or copper, zinc, manganese, and selenium in high available form, are really useful for the defense system of the udder. Fatty liver is the most frequent hepatic pathology in dairy ruminants: it is unavoidable the weight loss during the first weeks of lactation and that the liver does not transform all the fatty acids into energy. Choline and methionine are important for the export of fatty acids from the liver: they have a synergistic effect, facilitating the apolipoproteins synthesis that are limiting factors for the hepatic transport of fatty acids through very-low-density lipoproteins (VLDL). Carnitine is important to ensure the carnitine-acyltransferase synthesis, to improve NEFA transfer in the mitochondria to produce energy through oxidation.

Conclusion

Basal and functional nutrition can help to reach the health objectives that make the dry period indispensable. Choline, methionine, carnitine, and betaine in the rumen-protected form and the right dosage, are particularly important in farms with excessive BCS variation during the first weeks of lactation, where the average days of lactation are high because of the reduced fertility, and where the animals arrive at the dry-off too fat. Anti-oxidants supplementation of the dry period diet is useful in case of a high incidence of sub-clinical mastitis during the dry period and of placenta retention.For more information: marketing@vetagro.comOriginal article here.