dividi la lista in sottocategoria se non ci sono voci per quattro giorni ininterrottamente

Ecco un inizio per una possibile soluzione. Nota che sfortunatamente rimuove il primo oggetto, che dovrà essere risolto. Ma a parte questo, divide le liste in base al gap di 4 giorni

void Main()
{
    var data = new List<CowOutput> {
        new CowOutput {CowID = 1, DateOfMilking = new DateTime(2018, 7, 30), NumberOfMilkInLtr = 1.2F },
        new CowOutput {CowID = 1, DateOfMilking = new DateTime(2018, 7, 31), NumberOfMilkInLtr = 1.3F },
        new CowOutput {CowID = 1, DateOfMilking = new DateTime(2018, 8,  5), NumberOfMilkInLtr = 1.5F },
        new CowOutput {CowID = 1, DateOfMilking = new DateTime(2018, 8,  6), NumberOfMilkInLtr = 1.1F },
        new CowOutput {CowID = 1, DateOfMilking = new DateTime(2018, 8,  7), NumberOfMilkInLtr = 1.7F },
        new CowOutput {CowID = 1, DateOfMilking = new DateTime(2018, 8,  8), NumberOfMilkInLtr = 1.4F },
        new CowOutput {CowID = 2, DateOfMilking = new DateTime(2018, 7, 30), NumberOfMilkInLtr = 1.4F },
        new CowOutput {CowID = 3, DateOfMilking = new DateTime(2018, 7, 31), NumberOfMilkInLtr = 1.1F },
        new CowOutput {CowID = 2, DateOfMilking = new DateTime(2018, 8,  1), NumberOfMilkInLtr = 1.8F },
        new CowOutput {CowID = 5, DateOfMilking = new DateTime(2018, 8,  2), NumberOfMilkInLtr = 1.4F },
        new CowOutput {CowID = 6, DateOfMilking = new DateTime(2018, 8,  3), NumberOfMilkInLtr = 1.2F },
        new CowOutput {CowID = 2, DateOfMilking = new DateTime(2018, 8,  5), NumberOfMilkInLtr = 1.5F },
        new CowOutput {CowID = 1, DateOfMilking = new DateTime(2018, 6,  5), NumberOfMilkInLtr = 1.5F },
    };

    var cowId = 1;
    var days = 4;


    var cowData = data
        .Where(d => d.CowID == cowId)
        .OrderBy(d => d.DateOfMilking);

    cowData
        .Zip(
            cowData.Skip(1), 
            (current, next) =>
            {
                next.Group = (next.DateOfMilking.Subtract(current.DateOfMilking).TotalDays >= days)
                    ? current.Group + 1
                    : current.Group ;
                return next;
            })
        .GroupBy(d => d.Group)
        .Select(d => d.ToList())
        .ToList()
        .Dump(); // I'm using LinqPad to test this. You can remove this and just use the output.
}

public class CowOutput
{
    public Int32 CowID { get; set; }
    public DateTime DateOfMilking { get; set; }
    public Single NumberOfMilkInLtr { get; set; }
    public Int32 Group { get; set; }
}