Silage is a common form of roughage that allows the preservation of nutritional characteristics for prolonged periods (Jacobsen et al., Reference Jacobsen, Sørensen, Pedersen and Weiner2013; Cardoso-Gutiérrez et al., Reference Cardoso-Gutiérrez, Narváez-López, Robles-Jiménez, Morales Osorio, Gutierrez-Martinez, Leskinen and González-Ronquillo2020). In the Americas, corn silage (CS) is the most prevalent preserved roughage in dairy ruminant diets, however, its production is limited in some parts of the world due to land degradation and water scarcity (Jacobsen et al., Reference Jacobsen, Sørensen, Pedersen and Weiner2013). Therefore, alternative roughage resources with high crude protein (CP) content, digestibility, yield and reduced water requirements need to be explored for ruminant feeding (Wirsenius et al., Reference Wirsenius, Azar and Berndes2010; Jacobsen et al., Reference Jacobsen, Sørensen, Pedersen and Weiner2013). Sunflower (Helianthus annuus) includes 67 annual and perennial species that are extensively used for seed and oil production throughout the world (Tan et al., Reference Tan, Yolcu and Dumlu Gul2014; Aragadvay-Yungán et al., Reference Aragadvay-Yungán, Rayas Amor, Heredia-Nava, Estrada-Flores, Martínez-Castañeda and Arriaga-Jordán2015). Sunflower is drought-tolerant and cold-resistant due to its deep root system (Tan et al., Reference Tan, Yolcu and Dumlu Gul2014). It requires less water than maize and, as roughage, serves as a valuable source of protein and lipids (Demirel et al., Reference Demirel, Bolat, Çelik, Bakýcý and Eratak2009). It has been shown that sunflower silage (SFS) has an 80% similar feeding value to CS with higher crude protein and fat content (Tan et al., Reference Tan, Yolcu and Dumlu Gul2014). Hence, SFS is a viable alternative to CS as a feed source for ruminants, particularly in regions with limited water resources (Jacobsen et al., Reference Jacobsen, Sørensen, Pedersen and Weiner2013; Aragadvay-Yungán et al., Reference Aragadvay-Yungán, Rayas Amor, Heredia-Nava, Estrada-Flores, Martínez-Castañeda and Arriaga-Jordán2015). However, its ensiling may be difficult due to low dry matter (DM) content and a medium CP content that does not promote rapid lowering of pH (Demirel et al., Reference Demirel, Bolat, Çelik, Bakýcý and Eratak2009; Tan et al., Reference Tan, Yolcu and Dumlu Gul2014). With further development, SFS may become an alternative roughage for sheep, helping to mitigate climate change issues due to its lower water requirement (Wirsenius et al., Reference Wirsenius, Azar and Berndes2010). To our knowledge, no studies have investigated the effects of feeding CS, SFS and their mixture with concurrent use of in vitro and in vivo approaches. Therefore, we aimed to determine chemical composition, nutrient digestibility, nitrogen-balance and milk yield of dairy ewes fed on CS, SFS and their 50:50 mixture (CS-SFS).
Materials and methods
The research was carried out at the Animal Science farm of the School of Veterinary Medicine and Animal Science of the Universidad Autónoma del Estado de México, under the approved ID project UAEMex 4974/2020.
In vitro rumen gas kinetics and fermentation profile were assessed using three fistulated ewes and 96 h incubation of samples. The experimental procedures and data analysis are detailed in the online Supplementary File.
For the in vivo experiment, nine Suffolk × Texel dairy ewes (45 ± 6 (sd) days in milk, 79.9 ± 10 kg body weight, 0.55 ± 0.14 kg/d milk yield) were grouped in a replicated 3 × 3 Latin square design (n = 3), that included three 21-d periods of which 14 d were used for diet adaptation and the last 7 d for sample collection. The three dietary treatments consisted of forage (CS, SFS or their 50:50 mixture, CS-SFS) and concentrate (30% corn grain and 70% soybean meal) supplemented with vitamins and minerals (Multitec of Malta®; Celaya; Mexico). Diets with 50:50 forage to concentrate ratio were formulated to be isocaloric and meet NRC (2007) requirements of dairy ewes (online Supplementary Table S1). Forage and concentrates were manually mixed and offered twice per day (0800 h and 1600 h), with free access to water. Animals were kept in a roofed pen with individual metabolic cages (1.0 × 1.2 × 1.2 m) with slatted floor. Individual milk samples (100 ml) were collected at 16 : 00 h from 2 consecutive milkings and analyzed for fat, protein, lactose, total solids (TS) and non-fat solid (SNF) on an infrared milk analyzer (Milko Scan FT 200, Foss Electric, Hillerod, Denmark).
Statistical analysis
Data were analyzed in SAS 9.2 (SAS/STAT, SAS Institute Inc., Cary, NC) using a completely Latin square design, with the factors being the silage supplementation (n = 3) with the following equation:
$$Y_{ij} = {\rm \mu } + A_i + P_j + T_k + e_{ijkl}$$where Yij is the dependent variable, μ is the general average, Ai is the animal, Pj is the period, Tk is the silage supplementation treatment and eijkl the error term. Least square means (LSM) separation was performed using the PDIFF statement by Tukey's test and presented as LSM ± sem. Significance was declared at P ≤ 0.05.
Results
In this research communication, we focus on milk production and milk composition, while providing detailed information on in vitro gas kinetics and in vivo digestibility in the online Supplementary Material accompanying the paper. Briefly, in vitro trial showed that the highest total gas production, dry matter degraded substrate and microbial crude protein production (all significant, P = 0.001) was for CS, followed by CS-SFS (online Supplementary Table S2). Total intake of dry matter and organic matter were not altered by diets (P > 0.05, online Supplementary Table S3). However, the N balance was higher for SFS compared with both CS and CS-SFS (P < 0.05, online Supplementary Table S4). The highest milk yield was observed in CS group, followed by CS-SFS (P < 0.05, Table 1). However, fat corrected milk and protein and fat corrected milk were not affected by diet (P > 0.05). Similarly, feed efficiency estimations (namely energy corrected and fat and protein corrected milk yields in relation to dry matter intake) were not altered by diets (P > 0.05), but the highest (P < 0.05) milk yield:DMI was observed in CS-fed ewes. In terms of milk components, the concentration (g/100 g) of fat, lactose, total solids and protein was higher in CS supplemented ewes followed by CS-SFS (P < 0.05 or better). Likewise, except for fat yield (which was not altered), all milk component yields were higher in both CS and CS-SFS than SFS.
Table 1. Milk yield and components in dairy ewes fed diets based on corn silage (CS), sunflower silage (SF) and their mixture (CS-SFS)
FCM, fat corrected milk; FPCM, fat and protein corrected milk; ECM, energy corrected milk; DMI, dry matter intake; sem, pooled standard error of the mean.
Values are least-square means.
Within rows, different superscript letters indicate difference between diets (P ≤ 0.05).
Discussion
Global water scarcity, climate change, and food-feed-fuel competition constrain crop production in some regions, emphasizing the importance of efficient roughage use (Wirsenius et al., Reference Wirsenius, Azar and Berndes2010; Jacobsen et al., Reference Jacobsen, Sørensen, Pedersen and Weiner2013). SFS offers a valuable feeding source, however, there is still a lack of information on its usage as ruminant feed.
We showed that dietary inclusion of SFS was associated with lower in vitro degraded dry matter and microbial crude protein production which agrees with previous studies (Aragadvay-Yungán et al., Reference Aragadvay-Yungán, Rayas Amor, Heredia-Nava, Estrada-Flores, Martínez-Castañeda and Arriaga-Jordán2015) and is probably mainly related to the lower metabolizable energy and higher non-degradable fiber content of SFS. The lower in vivo digestibilities of dry matter and organic matter in SFS-fed animals may also be related to the higher fiber content of SFS that is consistent with previous data in dairy cows (Demirel et al., Reference Demirel, Bolat, Çelik, Bakýcý and Eratak2009). The inclusion of SFS in the diet of lactating ewes resulted in lower milk production as well as reduced lactose, total solids and protein contents. However, milk fat percentage was enhanced with SFS feeding. Even though milk production decreased in ewes fed SFS containing diets, fat and fat-and-protein corrected milk yields were not affected. This suggested that the inclusion of SFS led to improved milk fat content compared to CS. Higher milk fat in SFS fed ewes may be explained by the higher fiber content of the diet. In accordance with our results, Sainz-Ramírez et al. (Reference Sainz-Ramírez, Velarde-Guillén, Estrada-Flores and Arriaga-Jordán2021) reported that fat corrected milk (4%) was similar in dairy cows fed CS and SFS. Daily yield of milk components was different between diets and feeding SFS resulted in a significant reduction in daily production of protein, lactose and total solids. Lower daily lactose production can be explained by a reduction in diet fermentation (Ivan et al., Reference Ivan, Mir, Mir, Entz, He and McAllister2004). Milk protein production was closely linked to dietary CP, rumen fermentable carbohydrates and rumen microbial protein synthesis. Moreover, lower milk production is a factor limiting daily milk protein yield (Cardoso-Gutiérrez et al., Reference Cardoso-Gutiérrez, Narváez-López, Robles-Jiménez, Morales Osorio, Gutierrez-Martinez, Leskinen and González-Ronquillo2020). The higher milk protein of CS-SFS than SFS group may be related to the fact that this treatment may have been able to provoke rumen defaunation of ciliated protozoa that led to increases in rumen microbial synthesis of protein (Ivan et al., Reference Ivan, Mir, Mir, Entz, He and McAllister2004; Cardoso-Gutiérrez et al., Reference Cardoso-Gutiérrez, Narváez-López, Robles-Jiménez, Morales Osorio, Gutierrez-Martinez, Leskinen and González-Ronquillo2020).
In conclusion, dietary inclusion of SFS for lactating dairy ewes decreased milk yield, however, fat corrected and protein-and-fat corrected milk yields were not affected, and nitrogen balance was enhanced. In addition, milk fat percentage was enhanced with SFS. Overall, CS-SFS could be used as dietary roughage for dairy ewes as an alternative to the use of CS. Further studies should examine rumen function, milk fatty acid profiles and dairy product quality.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0022029924000293.
Acknowledgments
This research was partially financed by the Autonomous University of the State of Mexico (Project UAEMex 4974/2020).
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