Effects of Diets with Different Ratios of Neutral Detergent Fiber to Non-Fibrous Carbohydrates on Feeding Behavior in Transition Holstein Cows

The transition period is the most stressful time in the production cycle of dairy cows because of depressed DMI and marked changes in metabolism that support late gestation, parturition and the onset of milk synthesis (Drackley, 1999; Huang et al., 2014). The abrupt increase in energy demand and low DMI after parturition results in a negative energy balance (NEB) and DMI, rather than milk yield, is the major driver of NEB (Grummer et al., 2010). Earlier strategies focused on feeding energy-dense diets and maximizing DMI prepartum and were aimed at supporting development of the conceptus and mammary gland, and preparing dry cows for better adaptation to the early-lactation diet. In contrast, in the past 15 years studies have shown that over-consumption of energy prepartum often results in a slower increase in DMI postpartum when compared with cows on a restricted intake (Dann et al., 2006; Guo et al., 2007) or those fed a low energy diet containing wheat straw (Janovick et al., 2011).

The fiber content of the diet, as well as its physical characteristics such as particle size, density (Meel et al., 2016), fragility and digestibility, appear to be the main factors responsible for ruminal fill and daily DMI. The appropriate quantity of dietary fiber help to prevent the occurrence of ruminal disorders and promote healthy rumen functioning and productivity (Aschalew et al., 2019). Neutral detergent fiber (NDF), non-fiber carbohydrate (NFC) content and NDF: NFC ratios are used to express fiber content, carbohydrate composition, energy density and forage volume. A recent review suggested that the limiting factor for DMI is NDF digestibility and its relative rumen retention time (Fustini et al., 2017). The ruminal physical fill control system is more evident when cows are fed ad libitum because metabolic and endocrine signals are less effective at controlling appetite during early lactation (Allen and Piantoni, 2014). Therefore, larger volume rumen should be beneficial for improving DMI after parturition.

Monitoring individual feeding times, feed intake and feeding rates can provide useful information for dairy herd management, as changes in feeding behavior of dairy cows can be an indicator of health disorders (Bareille et al., 2003). The objective of the present study was to determine the effects of close-up dietary NDF:NFC ratios on DMI, feeding times, feeding rates and daily visits for transition Holstein cows fed ad libitum and housed in a free-stall barn.

Animals and design
 
Animal care and use were approved and conducted in accordance with the practices outlined in the Guide for the Care and Use of Agriculture Animals in Agriculture Research and Teaching (FASS, 2010). Thirty-nine multiparous Holstein cows were dried off at 60 d prior to expected parturition, and moved into an experimental barn which had 48 free stalls. Cows were grouped according to milk production in the first 3 months of the previous parity, body weight, body condition score and expected calving date and assigned randomly into 3 dietary treatments. All cows were enrolled in the experiment at the same time.

From dry-off to 22 d prior to expected parturition, all cows were fed the same far-off dry period diet (Table 1). From 21 d prior to the expected day of calving until parturition, cows were blocked and assigned randomly to three groups. Each group was fed either a low NDF:NFC ratio (1.03) diet (LF treatment, n=13), medium NDF:NFC ratio (1.38) diet (MF treatment, n=13) or high NDF:NFC ratio (2.08) diet (HF treatment, n=13) (Table 1). L. chinensis hay was initially broken into small particles, then mixed with corn silage and concentrate. The dry matter (DM) content of the three diets was adjust within 51%-52%. After parturition, all cows were provided with the same lactation diet to 35 d in milk (Table 1).


 
Cows were housed in a free-stall barn with delivery room and fed each diet as a TMR ad libitum throughout the experiment, specifically offered once (at 16:00) prepartum and twice daily (at 07:30 and 14:30) postpartum. Orts were controlled less than 8%. Diets were sampled weekly to determine DM contents and particle size distribution. Cows were milked 3 times daily.
 
Data collections
 
Feeding behavior was measured daily from -21d to +35 d by roughage intake control feeders (Insentec B.V., Marknesse, the Netherlands) with 48 feed bins. For each visit to the bin, the system recorded the cow number, bin number, initial and final times, weights and calculated the visit duration and intake (Chapinal et al., 2007). These measurements were used to calculate daily visits, DMI, daily feeding times, feeding rates and distribution of feed intake during a whole day.
 
Statistical analysis
 
Data were evaluated by One-Way ANOVA using SPSS 16.0 (SPSS Inc.). Least squares means were computed and are presented throughout. A value of P<0.05 was set as the significance level.

DMI
 
The average DMI decreased during the -3 weeks (Wk) and -2 Wk time periods as the NDF:NFC ratio increased (P<0.05; Table 2). There was no significant difference among the three groups in DMI during the last 48 h prior to parturition and HF diet fed cows had numerically higher DMI values compared to LF and MF diet fed cows in the final 24 h before calving (P>0.05; Fig 1). During -3 Wk to -1 Wk prior to calving, the average DMI for LF, MF and HF diet fed cows decreased 25.2%, 28.0% and 19.5%, respectively. The results revealed that a high-NDF diet caused a small change in DMI prepartum. Other study have also shown that diets supplemented with wheat straw can lead to lower DMI overall and declining DMI rates prepartum (Grummer et al., 2004). During the last 48 h prior to calving, DMI for cows in all three groups decreased dramatically from approximately 10 kg/24 h to approximately 5 kg/24 h. The results suggest that DMIs of dry period dairy cows can abruptly decrease in a short time frame before parturition regardless of the dietary NDF:NFC ratio. This sharp decrease in DMI can be used as a signal to monitor the upcoming delivery.

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The average DMI increased during the +5 Wk time period as the NDF:NFC ratio increased (P<0.05), but was not affected during the first four weeks of lactation and the first 48 h following parturition (P>0.05; Table 2; Fig 1). The long-term effect of increasing DMI can lead to less metabolic disorders, which could, in turn, decrease DMI. Some studies have demonstrated that over-feeding prepartum results in a greater number of health problems postpartum (Dann et al., 2006; Janovick et al., 2011). Cows achieved 72.7-75.2% of their calculated energy requirement during the first 4 weeks of lactation in a previous study (Huang et al., 2014). Therefore, early lactating cows mobilize triacylglycerols from adipose tissues to meet energy requirement. High contents of nonesterified fatty acids and β-hydroxybutyrate can result from excessive lipolysis and have negative effects on DMI (Huang et al., 2014; Huang et al., 2019).
 
Daily feeding time
 
The average daily feeding time prepartum was significantly affected by the prepartum NDF:NFC ratio (P<0.05), which were 149, 176 and 180 min/d for LF, MF and HF cows, respectively (Table 2). Another two studies reported average daily feeding times of 208 min/d during the final three weeks prior to calving (Yuan et al., 2015) and 179 min/d during the last week prior to calving (Proudfoot et al., 2009). This difference was mainly due to dietary NDF content and forage particle size. L. chinensis hay has high NDF (approximately 68%-74% DM) and acid detergent fiber (approximately 35%-40% DM) contents, and an effective ruminal NDF degradability of approximately 26%-31%. In the present study, the HF diet had a higher content of L. chinensis hay than the LF and MF diets, which can extend the feeding time of dairy cows. As NDF content increases, cows will typically spend more time for eating, have longer meal lengths and practice greater sorting behavior (Yang et al., 2001). It has been previously reported that a 1.8 h/d greater eating time when dietary forage content increased from 40% to 70% (Jiang et al., 2017). A recent review suggested that diets containing high forage content, especially if the fiber is lower in digestibility or has longer chop length, require greater time to eat and longer forage particle length also contributes to sorting (Grant and Ferraretto, 2018). Dairy cows tend to chew forages while eating just enough to swallow the bolus (Schadt et al., 2012). Generally, larger feed particles were chewed to a threshold size that was suitable for bolus formation and deglutition.

The average daily feeding time postpartum was not affected by the prepartum NDF:NFC ratio (Table 2; P>0.05). Other study have also reported that the daily feeding times for dairy cows were 150 and 173 min/d during the first and second week, which was similar to those observed in HF and MF cows in the present study (Proudfoot et al., 2009).
 
Feeding rate and visits
 
The average feeding rate prepartum for LF cows was higher compared with MF and HF cows (P<0.05) and the average feeding rate postpartum was not affected by the prepartum NDF:NFC ratio (Table 2; P>0.05). A previous study reported that the feeding rates of dairy cows were 95, 116 and 105 g/min in the time periods -1 Wk, +1 Wk and +2 Wk relative to calving, respectively (Proudfoot et al., 2009). These results are similar to those observed in LF cows in the present study in the -1 Wk and +1 Wk time periods relative to calving.

Increased NDF:NFC ratios raised the average visits during the -3 Wk time period (P<0.05) but had no effect (P>0.05) at -2 Wk and -1 Wk, as well as postpartum (Table 2). The average visits for cows in the three treatment groups were 37, 43 and 47, respectively, during the time periods -1 Wk, +1 Wk and +2 Wk relative to calving. It has been previously reported that the average visits for multiparous dairy cows were 32, 23 and 24 during the -1 Wk, +1 Wk and +2 Wk time periods relative to calving (Proudfoot et al., 2009), which was similar to our -1 Wk data but significantly lower than our data from the first and second week of lactation. Although HF cows had lower DMI at -3 Wk prior to calving, they had more visits compared with LF cows due to the diet containing more L. chinensis. Other study have also found that DMI per meal was greater for cows fed higher digestibility silage, but the number of daily meals was greater for cows fed lower digestibility silage (Miron et al., 2007).

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Distribution of DMI
 
Feeding once during prepartum or twice during postpartum, cows in all 3 treatments had higher percentages of DMI between 12:01-18:00 compared to those fed between 06:01-12:00, 18:01-24:00 and 00:00-06:00 (Fig 2). The increased NDF:NFC ratio was correlated with decreased (P<0.05) DMI between 00:00-06:00 prepartum and increased (P=0.09) DMI between 18:01-24:00. Other studies have also found that dairy cows had lower DMI between 00:00-06:00 (Wang et al., 2016), finishing steers spent more time on eating during day time than the night time (Yazdani and Hajilari, 2009).

Feeding diets with higher NDF:NFC ratio during prepartum resulted in lower DMI and feeding rates. Increased NDF:NFC ratio resulted in higher daily feeding times and visits prepartum and increased DMI during postpartum. There was no carryover effect of the close-up diet on daily feeding times, feeding rates and visits postpartum.

This research was financially supported by National Natural Science Foundation of China (31601964), Chongqing Research Program of Basic Research and Frontier Technology (cstc2018jcyjA1098) and Fundamental Research Funds for the Central Universities (XDJK2018C056).