Dairy cows are commonly fed total mixed ration (TMR) on commercial dairy farms. This feed practice has several advantages compared to providing the diet components separately, including higher dry matter intake (DMI) and lower sorting by the animals (Cooke et al., Reference Cooke, Monahan, Brophy and Boland2004; Bharanidharan et al., Reference Bharanidharan, Arokiyaraj, Kim, Lee, Woo, Na, Kim and Kim2018). In addition, an earlier study observed that the TMR in feed mixers promotes a particle size reduction (Bharanidharan et al., Reference Bharanidharan, Arokiyaraj, Kim, Lee, Woo, Na, Kim and Kim2018).
This reduction of the particle size (PS) can cause changes in the fermentation rate passing through the rumen, resulting in an increase in DMI, reduced ruminal neutral detergent fiber (NDF) degradation (Nasrollahi et al., Reference Nasrollahi, Imani and Zebeli2015; Haselmann et al., Reference Haselmann, Zehetgruber, Fuerst-Waltl, Zollitsch, Knaus and Zebeli2019) and possibly lower enteric methane (CH4) yield and intensity (Knapp et al., Reference Knapp, Laur, Vadas, Weiss and Tricarico2014). Some studies demonstrated effects of particle size promoted by chopping of the bulky forages on DMI (Yang and Beauchemin, Reference Yang and Beauchemin2006; Alamouti et al., Reference Alamouti, Alikhani, Ghorbani, Teimouri-Yansari and Bagheri2014), animal performance (Alamouti et al., Reference Alamouti, Alikhani, Ghorbani, Teimouri-Yansari and Bagheri2014; Ramirez et al., Reference Ramirez, Harvatine and Kononoff2016), ingestive behavior and mastication (Alamouti et al., Reference Alamouti, Alikhani, Ghorbani and Zebeli2009, Reference Alamouti, Alikhani, Ghorbani, Teimouri-Yansari and Bagheri2014), digesta passage rate (Ramirez et al., Reference Ramirez, Harvatine and Kononoff2016), ruminal fermentation profile and nutrients apparent digestibility (Alamouti et al., Reference Alamouti, Alikhani, Ghorbani and Zebeli2009, Reference Alamouti, Alikhani, Ghorbani, Teimouri-Yansari and Bagheri2014). However, only one study has reported the effects of particle size on CH4 yield (Wang et al., Reference Wang, Larsen, Weisbjerg, Johansen, Hellwing and Lund2022).
The effect of PS on ruminant feeding depends on many factors, such as the forage type, concentrate bulk ratio and feeding level (Tafaj et al., Reference Tafaj, Zebeli, Baes, Steingass and Drochner2007; Li et al., Reference Li, Beauchemin and Yang2020). To our knowledge, no studies evaluated the effect of PS and breed composition on CH4 yield and ingestive behavior under tropical conditions using crossbreeding dairy cows (Bos taurus × Bos indicus). The understanding of the effects of diet PS on Girolando ingestive behavior, animal performance and CH4 emissions is still unclear compared to Holstein cows. So, we hypothesized that the PS (short or long) affects the ingestive behavior, performance, and the CH4 emissions of Holstein and Girolando lactating dairy cows in a different manner. Thus, this study aimed to evaluate the effects of TMR particle size (length) and breed of cow on intake dynamics, performance and CH4 emissions in Holstein and Girolando lactating dairy cows.
Materials and methods
The study was performed at the Multi-use Livestock Laboratory of Bioefficiency and Sustainability, Embrapa Dairy Cattle, Minas Gerais, Brazil (21°33′22″S, 43°06′15″W). The procedures were approved by the Embrapa Dairy Cattle Animal Care and Use Committee (protocol n° 6250160316).
Experimental animals
Eight multiparous lactating cows (four Holstein cows with 636 ± 37.8 kg of body weight (BW) and four multiparous Girolando cows [½ Holstein × ½ Gyr]), (BW = 649 ± 62.4 kg), paired by milk production level (26.3 ± 1.29 and 14.0 ± 1.11 kg/d, respectively) and days in milk (DIM: 98.8 ± 1.89 and 97.0 ± 2.71 d, respectively) were used.
Experimental design and treatments
The experimental design was 2 × 2 Latin Square arranged as a crossover factorial scheme with two diets (short particle size, SPS or long particle size, LPS) and two breeds (Holstein and Girolando) comprising two periods of 26 d each (online Supplementary Fig. S1), where all data collection was performed at a cow level. Two particle size lengths of a diet based on maize silage, Tifton hay (Cynodon spp.), soybean meal, ground corn, and mineral mix were evaluated. The ingredient percentages used in the formulation were the same for both treatments (online Supplementary Tables S1, S2, and S3). The diets were formulated using the software Large Ruminant Nutrition System (version 1.0.29: Texas A&M University, Texas, Amarillo, USA; Fox et al., Reference Fox, Tedeschi, Tylutki, Russell, Van Amburgh, Chase, Pell and Overton2004) for supplying the maintenance and milk yield requirements (26.3 ± 1.29 and 14.0 ± 1.11 kg/d for Holstein and Girolando, respectively). Weekly, the dry matter (DM) of maize silage and Tifton hay was determined at 135°C for two h according to the method 930.15 (AOAC, 1990) to correct the proportions of the TMR. Feed samples (diet offered, refusals, and feces) were dried in a forced ventilation oven at 55°C for 72 h, ground (Wiley mill; A. H. Thomas) through a 1-mm screen sieve and grouped (DM basis) by period for each cow. Individual samples were analyzed for DM, OM, total N, ether extract (EE), and ash according to methods 930.15, 942.05, 984.13, 920.39, and 942.00, respectively (AOAC, 2005).
Intake and ingestive behavior
During the adaptation period and the last five days (day 21 to 26) of each experimental period, the cows were housed in a free stall barn equipped with individual automatic electronic bins (feeders, water drinker, and weighing device: AF-1000 Master Gate Intergado®, Betim, MG, Brazil) for measurements at cow level. Diets were offered at 0900 and 1600 h and to avoid sorting, the amount of feed was adjusted during the first 14 d of each period, calculating feed allowances with a goal of 5% refusals. To measure the DMI and digestibility, the cows were individually allocated to a tie-stall barn. From day 15 to 20 of each experimental period, individual cows' samples of the offered diet and refusals were weighed and collected for further analysis. In addition, the individual ingestive behavior was monitored using electronic bins (Intergado®, Betim, MG, Brazil) (Chizzotti et al., Reference Chizzotti, Machado, Valente, Pereira, Campos, Tomich, Coelho and Ribas2015).
Milk yield and composition
Cows were milked twice daily at 0700 and 1600 h, and the milk yield was recorded automatically using the Delpro Manager System software (DeLaval®, Delpro, Jaguariúna, SP, Brazil), equipped with electronic milk measurer MM23, controls MPC 580/680, and an automatic extractor for sampling milk. Milk yield and individual milk samples were collected daily in two sequential milkings (morning and afternoon) from the 15th to 26th day of the experimental period for measurements of milk composition.
Apparent total tract digestibility
The apparent digestibility of the DM, organic matter (OM), and nutrients (crude protein: CP, neutral detergent fiber: NDF, acid detergent fiber: ADF and non-fibrous carbohydrates: NFC) were estimated by total feces collection during five consecutive periods (day 15 to day 20 of each period).
Methane measurement
The CH4 yield and intensity measurements were performed using four open respiration chambers according to procedures described by Machado et al. (Reference Machado, Tomich, Ferreira, Cavalcanti, Campos, Paiva, Ribas and Pereira2016). The calculation of the CH4 emission was made using the air flux and the difference of the CH4 in the air entering (outside air) and leaving the chambers (Machado et al., Reference Machado, Tomich, Ferreira, Cavalcanti, Campos, Paiva, Ribas and Pereira2016).
Statistical analysis
Data were analyzed using the MIXED procedure of SAS where particle size, breed and interaction were used as fixed effects and cows (n = 8) nested within the period were the random effect. Data were tested for normality of the residues (Shapiro–Wilk; P > 0.05) after model fitting. The Kenward–Roger method was used to calculate the approximate denominator degrees of freedom. Means were compared using the LSMEANS/DIFF. Differences were considered significant when P ≤ 0.05. Additionally, Pearson's correlation analysis among k p and DMI was performed.
Results
Interaction between particle size and breed was significant for DMI where Girolando cows ate less LPS (P < 0.05; Table 1) than SPS. Particle size did not influence time spent at feed trough, eating rate, feed trough visits and visits with intake (P > 0.05; Table 1), even as no interaction was reported for any ingestive behavior response (P > 0.05; Table 1).
Table 1. Effect of the diet particle size (PS) and breed (B) on DM intake and ingestive behavior of DM
DMI, dry matter intake; SPS, short particle size; LPS, long particle size; sem, standard error of the mean; n.s., not significant. PS, effect of particle size (SPS vs. LPS); B, effect of breed (Holstein vs. Girolando); PS × B, effect of interaction between particle size and breed.
Within a row, means with different superscripts are different by Tukey test (P ≤ 0.05).
Passage rate (k p) was greater (P < 0.05; Table 2) in Holstein compared to Girolando (4.97 vs. 4.49%/h, respectively). Holstein cows had lower DM digestibility when fed a SPS diet, while Girolando cows had lower DM digestibility when fed LPS diet (P < 0.05; Table 2). Girolando cows had greater OM, CP, and NFC digestibility when fed SPS (P < 0.05; Table 2). Particle size did not influence milk yield or composition (P > 0.05; Table 3).
Table 2. Effect of the diet particle size (PS) and breed (B) on passage rate, DM, and nutrient apparent digestibility of dairy cows
k p, passage rate; DM, dry matter; OM, organic matter; CP, crude protein; NDF, neutral detergent fiber; ADF, acid detergent fiber; NFC, non-fibrous carbohydrates. SPS, short particle size; LPS, long particle size; sem, standard error of the mean; n.s., not significant. PS, effect of particle size (SPS vs. LPS); B, effect of breed (Holstein vs. Girolando); PS × B, effect of interaction between particle size and breed.
Table 3. Effect of particle size and breed on milk yield, fat-corrected milk, energy-corrected milk, milk composition, and feed efficiency of Holstein and Girolando cows
FCM, fat corrected milk; ECM, energy corrected milk; MUN, milk urea nitrogen. SPS, short particle size; LPS, long particle size; sem, standard error of the mean; n.s., not significant; PS, effect of particle size (SPS vs. LPS); B, effect of breed (Holstein vs. Girolando); PS × B, effect of interaction between particle size and breed.
Cows fed the diet with a SPS had lower CH4 intensity (−29.8%; P < 0.05). Also, Girolando cows had greater CH4 intensity (+42.4%) than Holstein cows (P < 0.05). Interaction particle size × breed was not detected for any parameter of CH4 emissions (P > 0.05) (Table 4).
Table 4. Effect of particle size and breed on CH4 production of Holstein and Girolando cows
SPS, short particle size; LPS, long particle size; sem, standard error of the mean; n.s., not significant. PS, effect of particle size (SPS vs. LPS); B, effect of breed (Holstein vs. Girolando); PS × B, effect of interaction between particle size and breed.
Discussion
Particle size had a distinct influence on the DMI, DM, and nutrient digestibility of Holstein and Girolando lactating dairy cows. Feed intake is regulated by the interaction between physical (retention time) and physiological mechanisms (e.g., osmolarity, hormone release: Allen, Reference Allen2014). Due to their greater milk yield, Holstein cows require more nutrients and energy than Girolando cows. In this scenario, the greater mammary nutrient uptake stimulates DMI, which is associated with a reduction of the available metabolites for liver oxidation (Allen, Reference Allen2014). Girolando cows, due to their lower milk yield, require a lesser quantity of nutrients for the mammary gland, resulting in a greater nutrient availability for liver oxidation and consequently reduction of the appetite (Allen et al., Reference Allen, Bradford and Oba2009; Allen, Reference Allen2014). It is interesting to note that Holstein cows did not exhibit a decreased DMI when fed LPS compared to Girolando cows, possibly due to the greater liver oxidation in Girolando cows fed SPS. Furthermore, this difference in DMI when fed SPS between breeds can also be attributed, in part, to increased rumen capacity in Holstein cows (Allen, Reference Allen2000). Haselmann et al. (Reference Haselmann, Zehetgruber, Fuerst-Waltl, Zollitsch, Knaus and Zebeli2019) demonstrated that Holstein Friesian cows fed a reduced particle size diet increased the DMI by 8.57%. The reduction in particle size most likely increased the pass-through reticulum-rumen of Holstein cows. However, it seems not to be a limitation for low levels of DMI (2.4% of BW) as observed on Girolando cows. Also, a previous study demonstrated that long particles (>1.18 mm) are 4.7-fold more sensitive to escaping the reticulum (Seo et al., Reference Seo, Lanzas, Tedeschi, Pell and Fox2009). Particle size reduction may increase the surface area, favoring ruminal degradation (Haselmann et al., Reference Haselmann, Zehetgruber, Fuerst-Waltl, Zollitsch, Knaus and Zebeli2019) as demonstrated in the current study, mainly for cows with lower DMI.
Girolando cows had greater eating rate, feed trough visits, and visits with intake compared to Holsteins. This means that a lower eating time meal can be associated with a greater eating rate, resulting in compensation during the meal. Conversely, faster meals promote increased ruminal distension and lower eating time (Allen, Reference Allen2014). In a previous study, Maulfair and Heinrichs (Reference Maulfair and Heinrichs2013) testing a SPS of maize silage, observed a decrease in eating time for the cows fed SPS compared to those provided LPS. Additionally, Girolando cows possibly had lower peaks of short-chain fatty acid production when fed SPS, although only butyric acid showed any effect of breed, given time for short chain fatty acid absorption.
Nasrollahi et al. (Reference Nasrollahi, Ghorbani, Khorvash and Yang2014) also observed an increase of eating rate of cows fed a SPS diet. The results of the present study suggest that for cows with lower intake capacity, such as the Girolando breed, TMR with SPS seems to be more beneficial and does not increase the risk of ruminal acidosis. Furthermore, for each extra meal frequency per day, DMI is predicted to increase by 0.19 kg/d. As a result, cows eating faster can consume 2.3 kg/d of DM more than others with lower meal frequency (Johnston and DeVries, Reference Johnston and DeVries2018).
Holstein cows had greater k p (+10.7%) regardless of particle size length compared to Girolando cows. This greater k p can be explained by their greater DMI. Additionally, a positive correlation between DMI and k p was observed (r = 0.85; P < 0.05). The total DMI k p was not estimated, but the k p of wet forage can suggest that in Holstein cows, feed remains less time in the rumen, which supports the digestibility results.
Holstein cows had lower DM digestibility on the SPS treatment, contrasting with Girolando cows. This can be explained due to rumen capacity and ingestive potential of the Holsteins compared to Girolando cows. Due to the great capacity and ingestive potential, when fed SPS, the feed probably passes through the rumen faster compared to LPS in Holsteins as observed in the study of Bauer et al. (Reference Bauer, Eghbali, Hartinger, Haselmann, Fuerst-Waltl, Zollitsch, Zebeli and Knaus2023). Feeding a reduced particle chopped hay potentiated by the increase of < 4.0 mm decreased DM and nutrient digestibility.
The NDF digestibility was not influenced by particle size or breeding. In contrast, Jiang et al. (Reference Jiang, Lin, Yan, Hu, Wang and Wang2018) did not observe any effect of particle size on DM or nutrient apparent digestibility. In general, the results of the current study demonstrate that the DMI level (Holstein = 3.1 vs. Girolando = 2.4% of BW) promotes a significant effect on rumen digestibility, assuming that the impact of the particle size on DMI is mainly associated with rumen passage rate (Tafaj et al., Reference Tafaj, Zebeli, Baes, Steingass and Drochner2007). Furthermore, previous studies demonstrated that decreasing the particle size of lactating dairy cows enhanced the rumen passage rate, resulting in an increase in DMI and a decrease in the NDF and ADF digestibility (Junck et al., Reference Junck, Tafaj, Zebeli, Steingaß and Drochner2005; Tafaj et al., Reference Tafaj, Zebeli, Baes, Steingass and Drochner2007).
The particle size did not influence milk yield or composition, except for MUN, regardless of the breeding. The same was reported by others (Coon et al., Reference Coon, Duffield and DeVries2018; Li et al., Reference Li, Beauchemin and Yang2020). This was expected, because particle size alone did not affect milk yield or composition (Tafaj et al., Reference Tafaj, Zebeli, Baes, Steingass and Drochner2007). Having said this, some studies have demonstrated greater milk lactose (Alamouti et al., Reference Alamouti, Alikhani, Ghorbani and Zebeli2009; Zebeli et al., Reference Zebeli, Ametaj, Junck and Drochner2009) and protein (Maulfair and Heinrichs, Reference Maulfair and Heinrichs2013). Classical studies suggested that milk composition is only influenced by particle size when the NDF concentration is close to or below the minimum level (25% of DM) recommended by the NRC (2001). In the current study, diets were formulated with 34% of NDF, justifying the lack of effect of the particle size on milk yield and composition.
The particle size reduction did not influence the CH4 yield but increased the CH4 intensity (g CH4/kg milk). Perhaps, an effect of the decrease in particle size would occur if there was a reduction in retention time capable of reducing the ruminal OM fermentation, especially the fibrous fraction (Beauchemin et al., Reference Beauchemin, Ungerfeld, Abdalla, Alvarez, Arndt, Becquet, Benchaar, Berndt, Mauricio, McAllister, Oyhantçabal, Salami, Shalloo, Sun, Tricarico, Uwizeye, De Camillis, Bernoux, Robinson and Kebreab2022). In part we cannot explain this increase in CH4 intensity for the SPS diets, while CH4 emissions are mainly due to the influence of animal performance, which impacts the CH4 intensity (Evans, Reference Evans2018). One possible explanation is that reducing particle size increases the surface area for microbial attachment, including ruminal fibrolytic bacteria, enabling rumen DM digestion and improving the final products (Zebeli et al., Reference Zebeli, Aschenbach, Tafaj, Boguhn, Ametaj and Drochner2012). CH4 intensity is related to the CH4 produced in the final product (milk yield, carcass yield, etc.), and cows producing more milk yield appear to dilute CH4 intensity. Girolando cows increased the CH4 intensity by 42.9% compared to Holstein cows. This increase is related to the lower milk yield of the Girolando cows, while for the Holstein cows, the CH4 was diluted by the greater milk yield, as discussed above.
In conclusion, Girolando cows increased the dry matter intake when fed a diet with short particle size, while the same did not happen in Holsteins. Dry matter digestibility increased in Holsteins when fed long particle size, while the opposite was observed in Girolando cows. Nutrient digestibility was reduced in Girolando cows when fed short particle size. Particle size did not influence eating time, eating rate, feed trough visits, visits with intake, milk yield and composition regardless of the breed. Reducing particle size increased CH4 intensity in both breeds.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0022029924000207
Acknowledgements
Authors are grateful to SEG/Embrapa, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and Fundação de Amparo à Pesquisa do estado de Minas Gerais (FAPEMIG).
