ffect of feeding lipogenic compared with glucogenic diets on feed intake, performance, and ruminal pH in transitional dairy cows

Transition period (3 weeks before to 3 weeks after calving) is a critical period for cows' health and production (Grummer 1995). During the late gestation, nutritional demand of fetus increases considerably, while feed intake reduces more than 30 percent during the last 3 weeks of gestation (Sadri et al. 2012). Nutritional strategies are important for preventing the decrease in DMI during close up period. On the other hand, rapid increase of postpartum DMI could reduce the severity of negative energy balance, and therefore, improve milk production and health (Poláková et al. 2010). Grummer (1995) reported a positive correlation between DMI at d 1 prepartum and d 21 postpartum. Several nutritional approaches for the close-up diet have been proposed to stimulate prepartum DMI and minimize lipid mobilization: 1) use of bulky forage NDF sources into the diet to increase ruminal fill, 2) increase in dietary fat or NFC content of the diet to increase energy intake, 3) use of appetitive feeds for increasing in DMI and preventing ruminal acidosis and 4) use of feed additives that serve as gluconeogenic precursors to increase energy supply (Dann, et al. 2007). These approaches have yielded variable results in research and production settings. Diets with high levels of NFC are more common, but these diets may lead to acidosis and feed intake depression (Wang et al. 2013). In addition, readily fermentable carbohydrates (i.e. barley grain), increase ruminal propionate production and propionate can lead to reduction e in feed intake (Allen. 2009). Beet pulp is a unique feed ingredient containing 40% NDF with highly soluble fiber content (especially pectic substances) (Dann et al. 2007). There are different results for replacing grains with dried beet pulp in dairy cows nutrition. Clark and Armentano (1997) reported an increase in DMI of cows after replacing of shelled corn with dried beet pulp. However, some researchers demonstrated that dried beet pulp had no effect on cows' milk yield (Mahjubi et al. 2009; Clark and Armentano 1997). Although, Mahjubi et al. (2009) with replacing 50% of barley grain with beet pulp reported an increase in milk fat percentage. This study was designed to investigate the effect of different form of non-fibrous carbohydrates (lipogenic vs. glucogenic) diets on feed intake, performance, and ruminal pH in transition dairy cows. All procedures were conducted under protocols approved by the Isfahan University of Technology (IUT), Laboratory Animal Care Advisory Committee. The experiment was conducted in Lavark at the Farm Animal Research and Teaching Unit of IUT. Twenty-four multiparous (1-3 parity) Holstein cows were kept in 9 m2 individual pens from 4 weeks before to 4 weeks after parturition. The animals have free access to feed and fresh water. In this study, pelleted beet pulp ground by a 2 mm screen was used as a partially replacement for ground barley grain. Twenty-four multiparous Holstein cows were fed a total mixed ration containing 100% barley as a grain source of concentrate and no beet pulp (BP0, Glucogenic Diet, GD) and in 2 experimental rations 25 (BP25, Low Lipogenic Diet, LLD) and 50% (BP50, High Lipogenic Diet, HLD) of barley grain in the glucogenic diet was replaced by beet pulp, from d 21 before anticipated calving to d 24 after calving. The experimental diets were formulated according to Cornell Net Carbohydrate and Protein System (CNCPS, v. 6.1, Cornell University, Ithaca, NY) for pre and postpartum periods. Data were analyzed as a block randomized design (parity as blocks). Daily DMI was determined by subtracting orts from offered TMR and were recorded for individual cows. After parturition, cows were milked three times daily in a milking parlour, and milk production was recorded at each milking time. Milk samples were collected weekly from three consecutive milking, and preserved using potassium dichromate. Milk samples were analyzed for fat, protein, lactose and total solid by an automated near infra-red spectroscopy analyzer (Milk-O-Scan, 134 BN, Foss Electric, HillerØd, Denmark). Body weights were measured weekly pre and postpartum (from d -28 to d +25) and the changes in BW were calculated. Postpartum net energy balance (NEB) for each cow was calculated based on NRC (2001). Results showed that during the prepartum period, DMI (kg/d), DMI (%BW), and energy intake (Mcal/d) were increased by substitution of barley grain with dried beet pulp (P<0.01); however, the change in DMI as a percentage of BW from d 19 to d 1 before parturition was not affected by treatments. During postpartum, DMI (kg/d), DMI (%BW), and energy intake (Mcal/d) increased as a quadratic effect (P<0.01) with the increasing levels of beet pulp replacement. Body weights, back fat thickness and postpartum calculated net energy balance were not affected by the treatments. During postpartum, milk yield was the lowest by using HLD (P<0.01). However, 4% FCM and ECM and total solid of milk were not affected by the treatments. HLD significantly increased milk fat percentage (P<0.05) and decreased milk protein percentage (P<0.07) in comparison with the GD and LLD. During postpartum, ruminal pH was the lowest in GD (P<0.05). Results suggest that using of LLD in periparturient diets increased DMI, energy intake, milk yield and improved rumen health.