Heat production and retained energy in lactating cows held under hot summer conditions with evaporative cooling and fed two rations differing in roughage content and in vitro digestibility

Abstract

The objective of this study was to measure the effect of feeding two total mixed rations (TMRs), differing in their roughage content and in vitro dry matter (DM) digestibility, on the physiological response and energy balance of lactating cows. The partitioning of metabolizable energy intake (MEI) between heat production (HP) and retained energy (RE) of cows held under hot weather conditions and external evaporative cooling was measured. In all, 42 lactating cows were divided into two similar sub-groups, each of 21 animals, and were fed either a control (CON) ration containing 18% roughage neutral detergent fiber (NDF) or an experimental (EXP) TMR containing 12% roughage NDF and used soy hulls as partial wheat silage replacer. The in vitro DM digestibility of the CON and EXP TMR was 75.3% and 78.6%, respectively (P , 0.05). All cows were cooled by evaporative cooling for 2 adaptation weeks plus 6 experimental weeks under hot weather conditions. The EXP diet reduced rectal temperature and respiratory rate of the cows while increasing their DM intake (DMI) from 23.1 to 24.7 kg/cow per day, milk yield from 41.9 to 44.2 kg and yield of energy-corrected milk from 38.7 to 39.7 kg, as compared with the CON group. Cows fed the EXP TMR had increased RE in milk and body tissue, as compared with the CON group, but the diets had no effect on the measured HP that was maintained constant (130.4 v. 130.8 MJ/cow per day) in the two groups. The measured MEI (MEI 5 RE 1 HP) and the efficiency of MEI utilization for RE production were also similar in the two dietary groups.

Effects of cooling dry cows under heat load conditions on mammary gland enzymatic activity, intake of food and water, and performance during the dry period and after parturition

“…No difference between treatments was found with respect to the average heart rate of the cows (Table 2) and this is in accord with a previous study in milking Table 2 Average ambient temperature, relative humidity and temperature humidity index (THI) in experiments 1 and 2 as measured in the morning (AM) and the afternoon (PM) during dry and close-up period. cows (Miron et al, 2008). Similar effect of evaporative cooling on decreasing the body temperature of dry cows was also demonstrated in a previous study (Wolfenson et al, 1988) but changes in respiratory rate have not been measured previously in studies using evaporative cooling of dry cows.…”

“…The THI elevation during day-time from 75 in the morning to 80 in the afternoon hardly affected cow's body temperature of the NC group (Table 2) since the cows responded to the environmental change by increasing their respiratory rate to get read of excess heat, as demonstrated previously in a study with milking cows (Miron et al, 2008). …”

“…The second group of 9 cows was located in the opposite side of the barn under heat stress conditions (NC). The parameters measured during the experiment included: rectal temperature, heart rate and respiration rate, measured in the morning (0800) and afternoon (1500) on a daily basis (Miron et al, 2008); DMI and water intake were measured in each tie-stall on a daily basis; body condition score (BCS) of cows was determined on a weekly basis (Ferguson et al, 1994). The mRNA levels of key enzymes in mammary and fat tissues explants were measured before parturition as described later.…”

Effect of feeding cows in early lactation with diets differing in roughage-neutral detergent fiber content on intake behavior, rumination, and milk production

“…These differences in TMR ingredients and their chemical compositions (Tables 1 and 2), were expressed in a greater intake per meal (by 13.3%, P = 0.03), a higher rate of meal consumption (by 23.2%, P = 0.02), a similar number of meals per day (7.92 and 8.35), a shorter daily eating duration (by 13%, P = 0.05), and a greater total daily DMI (by 7.2%, P = 0.02) in the EXP cows as compared with the CON cows (Table 3). Similar effects on rate of eating and daily DMI were obtained in previous studies that used soyhulls as a partial roughage replacement in TMR of midlactating cows (Miron et al, 2003(Miron et al, , 2008Adin et al 2008). Improvement of DMI in a similar feeding system was shown also by Weidner and Grant (1994).…”

“…Recently, we suggested increasing the voluntary energy consumption of the lactating cow by replacing part of the dietary roughage component with by-products rich in readily digestible NDF, such as soyhulls (Miron et al, 2003). In previous studies (Miron et al, 2003(Miron et al, , 2008Adin et al, 2008), we demonstrated that feed-ing dairy cows with soyhulls during midlactation as a partial roughage replacement increased DMI by 6.9% and milk yield by 5.5% (P < 0.05). However, there is a lack of knowledge on how the cow would respond to such a diet during the early stage of lactation.…”