The passage from the dry period (or the last weeks before calving in heifers) to the puerperium (the 20 days after calving) is really challenging for dairy cows. During this period (the transition period) there is a higher incidence of metabolic pathologies and of related infections. Metabolic pathologies during the transition (Figure 1) negatively affect milk production of the whole lactation, fertility, the immune system function, and the productive life of the animals. The most important risk factors for dysmetabolism are concentrated during the last 3 weeks before calving. Figure 2 highlighted the interconnections of the metabolic pathways: they are all risk factors for the other ones, affecting animal performance.
Figure 1: Most frequent metabolic pathologies and some of the reproductive pathologies related to the pregnancy and lactation period (Fantini, 2017).
Well-managed dairies, with available space, separate cows 3 weeks before calving, dividing primiparous and multiparous, preventing the stress of mixing older and younger animals. These dedicated spaces particularly care for dimension, hygiene, and temperature. The concentration of dietary protein and non-structural carbohydrates (i.e. starch and sugar) in the dry-diet increase: the rumen absorptive ability increases as well, in view of the high amount of volatile fatty acids that will be produced here with the lactation diet. The dietary management follows a steaming-up program. Three different diets are administered to the animals: one for the dry period, the second some days before calving, and the latest immediately after that. These diets have increasing nutrients concentrations to get the rumen and its microbiota used to them. The rumen takes no less than 40 days to adapt to a new diet.
Animals must be divided at least 20 days before calving, at 260 days of pregnancy for Holstein cows. Without management software, this evaluation is quite difficult and the most frequent error is the delay in moving. This delay can cause the regrouping of animals too close to the calving, in hot and overcrowded places, without dietary changing and adaptation. The worse combination is the short preparation of calving added to high nutrients concentrations in the diet. The consequence is a high risk of sub-clinical ruminal acidosis development, without clinical signs but that causes feed intake reduction, heavier than the physiological one, with a worse negative energy (NEBAL) and protein (NPB) balance. NEBAL and NPB lead to a strong weight loss of the animal after calving and to the excessive hepatic accumulation of fatty acids (high risk of fatty liver disease and sub-clinical ketosis even before calving). When sub-clinical ruminal acidosis and metabolic ketosis occur before calving, there is a high risk of clinical signs developing at the beginning of the lactation (fatty liver, abomasal dislocation, puerperal metritis, and mastitis, lower fertility).
Figure 2: Metabolic pathologies interconnections. (Fantini, 2005)
During the last 40-60 days of pregnancy, there is a high risk also for mineral disorders. Excess of calcium, phosphorus, and magnesium, and/or primary or secondary deficiency of magnesium, chlorine, and sulfur expose bovines to the risk of hypocalcemia and/or hypomagnesemia syndrome during the post-partum: the most relevant clinical sign is puerperal collapse. This metabolic pathology alters muscle and cell-mediated immune functions. Affected animals eat less, worsening the negative energy and protein balance, and have lower contractility of the nipple sphincters (with a high risk of mastitis) and of the uterus muscle (with a high risk of puerperal metritis).
With the correct transition management, the close-up is highly recommended: wide spaces, the possibility of access to the paddock, 20 days minimum duration, right temperature management. Clinical and functional nutrition has a pivotal role during the transition and the diet is hardly standardizable. The physiological feed intake lowering, that worsens during the last days of gestation (Figure 3), must be faced even without sub-clinical health problems. The higher nutrients concentration in the prepartum diet ensures a good intake of carbohydrates and proteins, minimizing the NEFA and ketone bodies production.
During the dry period, the rumen microbiota produces less volatile fatty acids and the ruminal villi are less stimulated. The aim of the increased dietary carbohydrate concentration is to stimulate butyrate and propionate production by rumen microflora, leading to the fast growth of ruminal villi (this process takes 6-8 weeks). Starch (its fermentation produces propionic acid, glucose’s most important precursor) supplementation maintains glycemia reducing ketone bodies and NEFA production. The exact amount of starch is not defined but many authors suggest 24%: however, this is a risky value if the close-up period is shorter than 20 days.
Figure 3: Feed intake per day before calving.
The dietary crude protein (CP) during the dry period is typically 12%: it ensures the correct rumen fermentation and MP intake. At the end of pregnancy, it is recommended to increase to 14% CP using the additional 2% in rumen-protected protein sources. To reduce NEFA and ketone bodies production, and maternal muscle protein loss, the suggested inclusion of rumen degradable protein is 60-65%, and soluble protein is 30-35% of the total CP. It is important to remember that amino acids are partially used for glucose production. Glucose requirement is about 1 kg/day at the end of pregnancy and increases at least to 2.5 kg/day after calving. The production of 58 g glucose involves 100 g of gluneogenetic amino acids. The most recommended feed additives during the transition are propylene glycol, rumen-protected methionine, and rumen-protected choline. Propylene glycol is an important source of propionic acid, the main glucose precursor: the minimum dosage suggested in transition cows diet is 300 g/head/day. Rumen-protected methionine is the most important limiting amino acid and avoids the excessive use of choline. This methyl donor is hardly involved in hepatic metabolism: choline deficiency is one of the most important predisposing factors for fatty liver.
- To prevent transition pathologies, dietary changing 20 days before calving, animal grouping, and environmental management (hygiene, temperature, number of animals) are strongly suggested;
- During the first 20 days after calving, it is important to separate cows from the rest of the herd, to intensify veterinarian visits, and add to the lactation diet ad libitum long fiber hay and sodium bicarbonate;
- Trace elements and antioxidant vitamins help against close-up oxidative stress;
- Rumen-protected methionine and choline dietary supplementation prevent hepatic damages due to fatty liver disease.