Feed chemical analysis
The basic ration of energy concentrate, wheat hay and barley grain (Table 2) is rich in dry matter and complex non-parietal sugars (starch and crude fibre), which, through anaerobic fermentation, lead to the ruminal production of acetate, butyrate, propionate and gases (carbon dioxide and methane). According to
Sauvant et al., (2011), these feeds should not be fed in excess, as this would lead to acidosis, fibrousness and dietary transition.
The basic ration (R1) of dairy cows, influenced by the energy concentrate, provides high proportions of crude lipids > to 6%. In the same comments of
Legato et al., (2014), such a practice is often accompanied by metabolic and nutritional disorders that alter the composition of the milk produced, more specifically the butyrous rate, increase the rate of long fatty acids and decrease the proportion of medium fatty acids. When the lipid content of the ration (Table 3) is controlled (feeding of R2, R3, R4 and R5 diets), the butter content of the milk is controlled; saturated fatty acid content decreases in favor of trans and polyunsaturated fatty acids of high nutritional value
(Ferlay et al., 2013). This proves that a balanced diet is an important lever for ensuring feed efficiency and increasing the quality of processable milk. In this approach, feed efficiency in dairy cows was observed according to the three criteria defined by
Hulsen, (2010) and
(Zaaijer and Noordhuizen, 2003), rumination time, rumen fill score and faeces. In practical terms, the R5 diet is best suited to lactating dairy cows, with a rumen filling score of 4 out of 5 (score scale defined by
Hulsen, 2010) giving good digestive transit without metabolic disorders and an ideal rumination time of 08 hours. The faecal assessment score was 1 out of 5 (on the score scale defined by
Zaaijer and Noordhuizen, 2003), an ideal score for lactating cows, giving bright faeces with a homogeneous consistency. No undigested elements were visible or palpable. This shows that the supplementation of the R5 ration ensured that the rumen flora functioned properly.
The nutrient content of a ration, as well as its structure, are important for good digestion and a healthy metabolism. A good feed ration must compensate for any energy deficits that dairy cows need to maintain their bodily functions. In addition, a controlled protein intake increases lactation requirements and improves milk quality. Fig 1 shows a difference in the proportions of energy and protein provided by the feed components used to formulate our rations. On the one hand, the high-energy base ration, made up of wheat hay, concentrated energy feed and barley grain (with a gross energy intake of between 237.96 and 303.65 Kcal). Secondly, the protein-rich forage supplement, made up of green grass silage and green meadow hay (with a protein content of between 11.45 and 17.5%).
In this study, excess energy intake of the basic ration has been substituted with a protein amendment provided by meadow hay and green grass silage.
These assessments concur with those of
Legato et al., (2014), Nozieres et al., (2007) and
Pawar et al., (2018) especially in the approach that dairy cattle require pasture forages rich in essential nutrients and low in energy. In amended rations, dairy cows break down the crude proteins in their feed (meadow hay and first-cut green grass silage) to build up their own proteins to maintain body mass and good lactation.
For example, the quality of the green feed given to dairy cows, combining green grass silage and green meadow hay, for organic farming and feeding
(Chaudhary and Thakur, 2021;
Santhosh, 2022) is reflected in the fine composition of the milk, which is preserved during cheese processing. This is a major improvement, as it guarantees the processor consistent milk quality right through to the finished product.
Chemical analysis and cheese-making properties of milk
Management of the fodder available on the farm and its use in a complementary ration (composed of green meadow hay and green grass silage) and the adoption of a period of acclimatization to improved diets, significantly conditioned the rise in milk production from 148.75 kg/day to 163.10 kg/day per experimental batch,
i.
e. from 29.75 kgs to 32.76 kgs per milked Holstein cow (Fig 2).
The aim of our study was to produce milk with the highest possible PR/BR ratio (>0.9 on average). Protein content is positively related to the general level of feeding
(Grelet et al., 2013). In present study, an increase of around 0.6 g of protein was observed per kg of milk produced (Fig 2). Dietary formulations have been made by shifting rumen fermentative orientations (volatile fatty acids) towards a reduction in the ratio of acetic and butyric acids to propionic acid and by improving nitrogen nutrition
(Grelet et al., 2013; Sauvant et al., 2011). In practical terms, the R5 diet best suited to the needs of dairy herd. Average milk production and chemical quality of milk from the different batches have been presented in Table 4.
After analysis of variance, the results found in this study for dry matter content, protein content, butyrate, lactose and mineral matter showed significant differences (p<0.05). This shows that green feed supplementation had an improving effect on protein content (3.38%) and total milk solids (12.78%). Milk protein concentration was high in the batch of cows on the R5 diet with 100% green feed supplementation. The average protein values of the bovine milk samples analyzed were estimated at 2.82% for batch T and increased from 2.88% in batch E1 to 3.38% in batch E4 (Fig 2). These results are in line with the mean values obtained by
Tir et al., (2015) and lie within the variation range of
Matallah et al., (2017) (from 2.7 to 3.4%). Improving diets with protein-rich green fodder significantly improved the PR of milk of technological interest, an indicator of good experimental herd management and applied feeding practices.
The milkfat content is controlled within a range of 2.5 to 3%, which is an appropriate technological parameter for a cheese standardized in fat on dry matter (F/D of 40 to 45%), giving the cheese typical organoleptic characteristics : flavor, taste and above all texture. Results concur with those of
Vignola and Amiot (2002) and
Ferlay et al., (2013).
In experiment, there was no significant difference in lactose content. Values ranged from 4.42 to 4.37%± 0.01 for lot T and lot E, respectively. The average lactose content of the cow’s milk analyzed was estimated at 4.4%. Lactose, the main sugar present in milk and a lactic fermentation substrate for lactic acid bacteria, is within the normal range for cow’s milk,
i.
e. from 4.2% to 5.2%
(Grelet et al., 2013).
pH values ranged from 6.68 to 6.73±0.02 for batches T and E, respectively. These values are comparable to those of milk of the same breed from other regions of the country as reported by
Maatallah et al., (2017); by
Remane et al., (2016) and by
Tir et al., (2015). These results are also close to the range (6.5 - 6.85) established by
Tahlaiti et al., (2020). According to
Lij et al., (2006), milk pH varies from one diet to another and depends, for a given herd, on the richness of its milk in certain constituents, particularly minerals and insoluble proteins, caseins. In cheese-making technology, any drop in pH below the norm favors the solubilization of minerals and the destabilization of casein micelles, leading to excessive losses in the whey during processing, with a direct influence on the quality of the cheeses produced
(Colinet et al., 2013).
The mineral fraction of milk plays an important role in dairy technology and particularly in cheeses. Indeed, any change in mineral distribution has an impact on the technological properties of milk and the rheological properties of coagulum
(Grelet et al., 2013). According to the results, the mineral content is 0.59% in the basic ration and rises from 0.64 to 0.85% in rations amended with the progressive incorporation of green fodder (green grass silage and meadow hay). According to some authors, dairy cows with a well-balanced and well-managed diet produce milk, depending on the lactation phase, with variable proportions of mineral matter ranging from 0.6 to 0.9%
(Hurtaud et al., 2001). The mineral balance between the colloidal and milky phases depends on pH, ionic strength and temperature. Any failure will result in an imbalance in this mineral fraction.
Measuring urea in milk is another indicator of feed efficiency, making it possible to monitor the protein intake of dairy cows
(Nozieres et al., 2007). Interpretation of the results obtained provides information on ration balance. The average urea content of cow’s milk in experimental animals fed different diets ranged from 182.35 mg/l to 251.64 mg/l. Low urea levels in milk (< 200 mg/l) may reflect a lack of ammonia in the rumen, resulting on the one hand from low crude protein levels in the base ration and on the other from rumination failure leading to ammonia losses. Rumen microflora are unable to capture ammonia and convert it into protein
(Hurtaud et al., 2001). The milk obtained from experimental cow batches E2, E3 and E4, on a diet improved by the incorporation of green forages (green grass silage and meadow hay) combined with good rumination, show urea levels > to 200 mg /l and < to 350 mg/l, showing that the feed ration is balanced. According to
Nozieres et al (2007), a controlled urea level maximizes protein yield and minimizes the release of nitrogen in the form of urea in the urine.
The results of the analysis of variance showed that there was a significant difference. According to
(Bir et al., 2015; Hurtaud et al., 2001; Legato et al., 2014; Matallah et al., 2017), there is a direct relationship between basal nutritional status and the diet improved by green feeding and the ingestion of nutrients with high biological value. The supplementary ration ensured a dietary balance between the protein and carbohydrate fractions in the diet to improve rumen fermentation and the balance of nutrients needed needed to maintain dairy cows in lactation with the production of milk of good technological quality.
Controlling the cheese-making potential of dairy products
Coagulation of milk by lactic acidification and/or enzymatic activity (rennet) is the first stage in cheese-making, which can be considered as the result of a process of concentration of casein and fat after elimination of whey. For the cheesemaker, the behavior of the milk during coagulation plays an important role in the success of the cheese-making process
(Lij et al., 2006; Vignola and Amiot, 2002).
In this respect, the technological coagulation time gave an average flocculation time of 12.3 minutes for milk from the control batch, compared with average times ranging from 5.28 to 9.4 minutes for milk from experimental batches, against an average setting time of 25.1 minutes for the control batch and setting times ranging from 10.96 to 19.02 minutes for milk from experimental batches (Fig 3). The coagulation standard for milk, applicable by the laboratory (LSTPA), should be 5 minutes for flocculation time and 10 minutes for setting time. The results obtained (on Fig 3) are not compatible with milk from the control batch and are consistent with satisfactory to favorable coagulation activity and kinetics for all cheese processing of milk from experimental batches fed diets enriched with high-protein green fodder.
Cheese curds are formed by the agglomeration of caseins
(Lij et al., 2006). A good protein content in milk ensures faster curdling (coagulation), a firm gel that holds together better and retains matter better and therefore better cheese yield.
Statistical analysis using Systat Software Mystat 13 to assess the similarity of the averages of the diet formulation results and the quality of the milk produced, yielded significance values with a significant P<0.05. The R5 diet formulation was best suited to milk production and the cheesability of the milk obtained. Dairy farming practices substituting energy concentrate with a high nutritional value forage diet based on selected pasture:
- Ensured feed efficiency.
- Maximised the individual performance of prim holstein dairy cows.
- And have given the milk a fine composition with good cheese-making qualities.
